08:00 - 08:30
08:30 - 09:00
08:30 -
ESA Opening
Arino, Olivier - ESA-ESRIN, Italy
presentation
08:45 -
UCM Context and Objectives
Rio, Marie-Hélène - ESA/ESRIN, Italy
presentation
09:00 - 10:15
09:00 -
In-situ Observations of Ageostrophic and Submesoscale Ocean Currents
Lumpkin, Rick - NOAA/AOML, United States of America
In-situ observations from surface drifting buoys and from point acoustic meters of the global tropical moored array are invaluable to better describe and understand ocean circulation, particularly at the short time and space scales describing the submesoscale and ageostrophic components of the flow field not well resolved in satellite measurements, including the near-equatorial region. Thse observations are also a unique tool for validating state of the art ocean circulation products, and for better understanding their gaps.
09:15 -
Surface Currents In High Resolution Ocean Circulation Models : Current Status And Observational Requirements.
Le Sommer, Julien (1);
Brodeau, Laurent (2);
Albert, Aurélie (1);
Molines, Jean-Marc (1);
Ajayi, Adekunle (1);
Leroux, Stéphanie (2);
Brankart, Jean-Michel (1);
Brasseur, Pierre (1);
Verron, Jacques (1,2);
Penduff, Thierry (1);
Barnier, Bernard (1) - 1: CNRS, France;
2: Ocean Next, France
High resolution ocean circulation models are now able to simulate explicitly ocean dynamics at basin to global scale down to kilometric resolution. Such submesoscale permitting ocean simulations provide relevant information for preparing satellite observation missions, for designing future operational prediction systems and for designing multi-mission high level products merging different sources of observational data. But the computational cost of submesoscale permitting models and the coverage of high resolution observations challenge our ability to evaluate systematically these models and to improve their skills through sensitivity analyses.
In this presentation, we will review the current skill of NEMO ocean circulation model, used in most CMEMS forecasting systems, in terms of the representation of surface currents at fine scales (1-50km). Our presentation will in particular focus on results of a series of North Atlantic 1/60° model simulations (eNATL60) performed in preparation for the upcoming SWOT altimeter mission. We will describe NEMO model skill with respect to the representation of surface current and discuss its main present limitations. The presentation will also highlight relevant ongoing activities within the frame of IMMERSE H2020 project which aims at improving NEMO ocean model’s skill at kilometric resolution. Observational requirements for improving simulated surface currents in ocean circulation models and for initializing limited-area, short-term ocean forecasts at kilometric resolution will also be discussed.
09:30 -
The Globcurrent project: Achievements and Roadmap
Johannessen, Johnny A. (1);
Chapron, Bertrand (2);
Collard, Fabric (3);
Rio, Marie-Helene (4);
Gaultier, Lucile (3);
Nocioli, Francesco (4);
Quartly, Graham (5);
Donlon, Craig (6) - 1: NERSC, Norway;
2: Ifremer, France;
3: OceanDataLab, France;
4: ESA/ESRIN, Italy;
5: Plymouth Marine Laboratory, United Kingdom;
6: ESA/ESTEC, Neatherlands
The GlobCurrent project (http://www.globcurrent.org) aims were to: (i) advance the quantitative estimation of upper ocean surface currents; and (ii) demonstrate impacts in user-led scientific, operational and commercial applications.
As advocated and demonstrated in this GlobCurrent project, a synergy approach combining diverse satellite sensor observations with in-situ measurements can partially fill existing spatial-temporal observations gaps at the mesoscale to sub-mesoscale. Through this approach, the GlobCurrent project has strengthen the knowledge of upper ocean mesoscale features. However, outstanding challenges remain to assess the relative roles of the horizontal and vertical shears that generate these transient and dynamic upper ocean features. Looking ahead, new missions such as the Surface Water and Ocean Topography (SWOT), Sea-surface Kinematics Multiscale monitoring (SKIM) candidate Mission and sensors that will herald a new era in Doppler retrieval-based oceanography will strengthen the multi-modal EO sensor synergy and thus fill critical spatial-temporal observation gaps. In turn, we expect to gain better insight on how mesoscale features and processes influence air-sea interaction as well as the energy pathways, buoyancy budgets, vertical motions and physical-biology interactions in the upper ocean.
09:45 -
Preparing for Future Fine-scale Ocean Observations of Surface Topography and Surface Currents
Morrow, Rosemary - LEGOS - CNRS/CNES/IRD/University of Toulouse, France
Recent advances have improved our understanding of satellite altimetry observations over the ocean, for the detection of fine-scale ocean dynamics. Altimetry measures sea surface topography, directly related to the depth-integrated ocean pressure field, and surface currents can be derived for larger scales under the assumption of geostrophy. Different satellite radar altimetry techniques are being used today at high-resolution over the open and coastal oceans: from conventional alongtrack nadir altimetry in Ku-band (Jason) and Ka-band (Saral) to alongtrack Synthetic Aperture Radar (SAR) at nadir (Cryosat-2 and Sentinel-3). Their alongtrack error levels vary geographically and seasonally and will limit the effective sea surface height (SSH) scales that can be resolved. Many high-frequency signals from tides, internal tides and internal gravity waves are also observed with altimetric SSH but are not in geostrophic balance. Techniques to estimate and separate these high-frequency signals from the altimetric SSH data will be discussed. Various mapping techniques are also being explored to derive gridded SSH data and derived geostrophic and cyclo-geostrophic currents at finer-scales for open ocean studies and in the coastal zone.
We have particular interest in the ocean dynamics that have a SSH signature in the wavelength scale of 15-200 km, including small mesoscale structures, larger submesoscale fronts and filaments, and internal tides and internal gravity waves. These are difficult to observe with the present altimeter constellation, due to the large gaps between groundtracks and alongtrack noise levels. The future global SAR-interferometry mission, SWOT – Surface Water Ocean Topography, will be launched by NASA/CNES in 2021. SWOT aims to measure terrestrial surface waters and ocean SSH over a wide swath, and provide the first 2D observations of SSH on a 1-2 km grid. The low noise level of the SWOT observations should allow us to observe physical processes in the open and coastal oceans with wavelength scales down to 15-40 km, depending on surface conditions. We will address how the fine-scale ocean SSH will be observed with the future SWOT mission, and the challenges in mapping the SWOT swath SSH observations to derive ocean currents. As with all altimeters, SWOT SSH will give us important information from dynamical processes below the surface mixed layer. There will be interesting synergy in combining SWOT with other 2D satellite data such as SST, ocean colour or SAR images, or with in-situ current observations, to better understand the oceanic exchanges between surface mixed layer processes and the deeper ocean.
10:00 -
SKIM, a Candidate Satellite Mission Exploring Global Ocean Currents and Waves
Ardhuin, Fabrice - LOPS, France
The Sea surface KInematics Multiscale monitoring (SKIM) satellite mission is designed to explore ocean surface current and waves. This includes tropical currents, notably the unknown patterns of divergence and their impact on the ocean heat budget near the Equator, monitoring of the emerging Arctic up to 82.5$^{\circ}$N. SKIM shall also make unprecedented direct measurements of strong currents, from boundary currents to the Antarctic circumpolar current, and their interaction with ocean waves with expected impacts on air-sea fluxes and extreme waves. For the first time, SKIM will directly measure the ocean surface current vector from space using two complementary methods: Doppler pulse-pair and Delta-K. The main instrument on SKIM is a Ka-band conically scanning, multi-beam Doppler radar altimeter/wave scatterometer that includes a state-of-the-art nadir beam comparable to the Poseidon-4 instrument on Sentinel 6. The well proven Doppler pulse-pair technique will give a surface drift velocity representative of the top two meters of the ocean, after subtracting a large wave-induced contribution. The two horizontal components of near-surface currents vectors will be obtained with an accuracy better than 7 cm/s for horizontal wavelengths larger than 80~km and time resolutions larger than 15 days, with a mean revisit time of 4 days for of 99\% of the global oceans. For the first time from space, SKIM will attempt to measure vertical shear in the upper 10~m of the surface ocean using delta-K processing, similar to a multi-frequency High Frequency coastal radar. Both techniques, will provide unique and innovative measurements that will further our understanding of the transports in the upper ocean layer, permanently distributing heat, carbon, plankton, and plastics. SKIM will also benefit from co-located measurements of water vapor, rain rate, sea ice concentration, and wind vectors provided by the European operational satellite MetOp-SG(B), allowing many joint analyses. SKIM is one of the two candidate satellite missions under development for ESA Earth Explorer 9. The other candidate is the Far infrared Radiation Understanding and Monitoring (FORUM). The final selection will be announced by September 2019, for a launch in the coming decade.
10:15 - 10:45
10:45 - 12:00
10:45 -
Industry User Requirements for Ocean Current Information
Jeans, Gus - Oceanalysis Ltd, United Kingdom
User requirements for ocean current information will be described, with a focus on various offshore industries. The presentation will summarise relevant initiatives of the IMarEST Operational Oceanography Special Interest Group (OOSIG) and personal research. A defining activity of OOSIG is to improve engagement between users and suppliers of ocean information. This is mainly achieved through the Oceans of Knowledge conference series, which explores a wide range of user case studies. Highlights from these events will be presented, considering the requirements of users including offshore energy, shipping, aquaculture and leisure. This presentation will also draw upon extensive professional experience in commercial oceanography. Relevant personal research includes new methods to quantify internal wave velocities and an application focussed review of ocean surface currents. The impacts of internal waves on offshore industry will be briefly summarised. These impacts are categorised as rapidly varying ocean currents in metocean practice. This summary will provide context to a new development, aimed at deriving internal wave characteristics from satellite data, outlined in a different abstract submitted to the WOC2019 event. The surface current review builds on industry requirements presented at the ESA ESTEC workshop in May 2013. Relevant contributions to a comprehensive review paper, drafted with other authors, will be presented. The paper aims to provide an application focused review of ocean surface current mechanisms, measurement techniques and modelling approaches. Key motivations include fundamental difficulties in reliable measurement and the persistent lack of a widely held consensus on the definition of surface currents.
11:00 -
The Use Of Ocean Currents For Oil Spill Monitoring (Oil Transport & Weathering Modeling)
Gouriou, Vincent - Cedre, France
Cedre's vocation is to provide advice and expertise to spill response decision-makers. This mission covers both marine and inland waters, and involves all types of pollutants (oil, HNS, etc.). Cedre's services and expertise can be provided to French or foreign authorities as well as to private organizations. French operational capacity in oil spill drift forecast is based on Meteo France and Cedre expertises. Drift forecasts rely on a pollutant drift model, named MOTHY. Cedre and Meteo France have been working together for many years (since 1996) to develop and improve MOTHY.
When a disaster occurs, authorities aspire to a faster and more effective management of pollution to limit the consequences. To this end, French authorities which take response measures for health or economic protection during a marine pollution incident need efficient software tools to assess the risks related to marine pollution. This allows them to quickly set up a relevant safety area, the aim being to protect the populations and the environment, to mobilize the appropriate response tools and to anticipate the situation in the short or medium term. In case af major oil spill, a French Slick Drift Monitoring and Prediction Committee is implemented, which include Cedre, Ifremer, MRCC, French Navy, Meteo France and possibly several Met offices. These organisations are in charge of obtaining and analysing all relevant data from models in order to make an assessment of how the pollution will spread.
There are differents types of models :
Oil weathering models predict the changes in oil characteristics that may occur over time, under the influence of a variety of environmental conditions.
Trajectory or deterministic models are used to predict the route of an oil slick over time.
Stochastic models, which are also known as probability models, show the probability of where an oil spill may impact for defined time periods. Historical wind records that contain the frequency of wind speed and direction are required.
Hind-cast models, sometimes known as backtrack models, reverse the trajectory modelling process. These can be used to estimate the spill origin in situations where the source or release point is unknown.
Hydrodynamic data, which ideally should include both tidal and residual currents, together with wind data and average sea surface and air temperatures are required by most oil spill models. Hydrodynamic data is the most important parameter as it has the greatest influence on oil migration (oil moves with 100% current and 3% wind), however it is often the most difficult dataset to acquire.
In 2019, Cedre is going to carry out a model comparative study for oil spill model and would be interested in including different currents datasets such as Globcurrent products.
11:15 -
Current Matters; Developing Communities Of Practice For Fisheries And Aquaculture Spatial Data Management.
Ellenbroek, Anton (1);
Taconet, Marc (1);
Pagano, Pasquale (2) - 1: FAO of the UN Italy;
2: CNR-ISTI Italy
The monitoring of marine fisheries, aquaculture and areas can improve with accurate, timely, and interoperable data. The communities that use these data have very wide ranging needs, and have to collaborate to combine data from many sources, including biodiversity, bio-physical observations, fleet and land registries, socio-economic data and space based observations of waves, colour, currents, etc.
FAO Fisheries Department is particularly interested to improve the lives of coastal communities (SDG2) and the sustainable expoitation of marine resources (SDG14). Data from space-based circulatation models, but also the forecasts derived from them, will help the FAO communities (e.g. the iMarine community) to understand and refine the study of the relationships between human activity and the envrionment.
With the assistance of several EU projects, and supported by an EU Scientific Infrastructure D4Science, the iMarine community merges data to develop cross-domain analysis of their areas of interest.
The iMarine community is curently developing services and / or proposals to further use marine circulation data for:
Where some of these services are already avaialble, others still need to be refined. The iMarine initiative seeks to make them useful for use by communities that want to merge the information with either environmental model simulation data, or with socio economic data. This appraoch will be explained with several examples from the aquaculture domain.
11:30 -
EMEC - Metocean Data Requirements, Collection and Challenges
Darbinyan, David - The European Marine Energy Centre Ltd, United Kingdom
The European Marine Energy Centre (EMEC) is the first grid-connected test site for Tidal and Wave Energy Devices. Since the founding of the centre more energy devices have been tested on its sites than on any other site around the world.
Located on the Orkney archipelago to the north of mainland UK, the test centre’s wave site in Billia Croo is exposed to virtually unlimited fetch from North Atlantic, providing a significant energy resource as well as challenging conditions to test the device performance and survivability. At the same time strong tidal flow in the inter-island channels provides an excellent resource for EMEC’s full scale tidal energy device test site at the Fall of Warness. Apart from the two full-scale sites, the centre also provides access to two sheltered ‘nursery’ sites for non-grid connected, scaled device testing.
During 15 years of operating, a large amount of metocean data has been collected at EMEC. The data collected includes: over 10 years of continuous wave observations at Billia Croo from several Waverider buoys; a large number of ad-hoc current profile observations at tidal and wave test sites; and years of data collected using meteorological stations installed near substations on-shore. In addition, X-band radars have been installed and are currently being calibrated. The collected in-situ observations are complemented by Orkney-specific hindcast datasets used to derive long-term metocean characterisation of the sites.
Despite the large amount of observational and model data available, there are still challenges in the data space including: continuous real time wave data collection in a presence of a strong tidal flow; observations of surface currents with high spatial resolution; high spatial resolution wave field evolution in the presence of Wave Energy Devices; and continuous historical wave, water level and current observations for hindcast model validation.
11:45 -
Optimizing ship routing
Dol, Mélanie (1);
Dussauze, Morgan (1);
Collard, Fabrice (2);
Gaultier, Lucile (2);
Rapp, Jocelyn (3) - 1: ACTIMAR, France;
2: OceanDataLab, France;
3: CMA CGM, france
In a prospect of Blue Economy and Blue Growth, optimum ship routing is a major challenge. The goal is not to avoid all adverse weather, waves and current conditions but to find the best reliable balance to minimize time of transit and fuel consumption and reduce emissions without placing the vessel or crew at risk
For a few years, Actimar has worked with shipping companies to help them finding the best route based on the marine weather analyses and forecasts including wind, wave and surface current conditions, ship characteristics and cargo requirements. The reliability of surface current forecast is a real issue. The actual field conditions are almost unknown. Actimar has developed a decision support service aimed at providing the most accurate surface current field along with a confidence index estimated from comparison between ocean forecasts and in situ observations.
The TOPVOYS project from MarTERA (ERA-NET COFUND), led by NERSC and its six partners from Norway France and South Africa, is aiming at improving the service, in particular by exploiting all the available Earth Observation data into the model qualification process. Amongst the French partners, OceanDataLab will provide a software plateform dedicated to satellite data analysis and interfaced with the qualification process developed by Actimar. As an end-user of the project, CMA CGM will qualify the improvement of the service by testing the new products into their ship routing software.
12:00 - 12:10
Drift at Ocean Surface: Environmental and Maritime Safety Case Studies.
Dufau, Claire
Sutton, Marion;
Mercier, Franck;
Granier, Nicolas;
Lucas, Marc;
Dufau, Claire - Collecte Localisation Satellites (CLS), France
Most of the marine economy sector relies on human activities taking place at the ocean surface: maritime transport, fisheries, oil & gas exploitation, maritime tourism.
On one side, maritime transport, fisheries, oil & gas exploitation, maritime tourism are threatened by the ocean surface conditions (extreme winds, waves, currents). In case of human overboarding or ship in distress, surface currents, tides and winds play a primary role in their transport at the surface. Search and rescue campaigns can rely on drift estimation at ocean surface to fasten the recovery and increase lifesaving. Natural phenomena also harm marine activities at ocean surface through drifting threats: Sargassum algae rafts in Caribbean Seas or icebergs in polar oceans can be detected by satellite and their future pathways estimated by drift modeling for sidestepping.
On the other side, maritime transport, fisheries, oil & gas exploitation, maritime tourism are at their turn threatening the ocean by spreading pollutants at its surface (oil seepages, garbage, waste water, containers). Once at sea, these pollutants are transported by surface currents, tides and winds and estimating their drift at ocean surface is crucial for cleaning campaigns or protection deployment.
For protecting marine and coastal environments, as well as for ensuring maritime safety, drift modeling estimation constitutes an efficient decision tool.
This communication will present our drift modelling service MOBIDRIFT and its use in actual drift scenarios for environmental monitoring (oil spill, Sargassum algae) and security purposes (Iceberg, Search&Rescue).
Mercator Ocean - Highly Qualified and Customized Oceanographic Service for Traditional Shareholders Downstream Applications
Landes, Veronique;
Tressol, Marc;
Durand, Edmée - Mercator Ocean International, France
Mercator Ocean has acquired the capacity to provide highly qualified and personalized oceanographic services to its shareholders and associated entities. This story, fruit of fifteen years of user service experience, began in 2003, with the first on-going service for the SHOM, one of its five historical shareholders with CNRS, Ifremer, IRD, and Météo-France. This support translates into the implementation and follow-up of tailor-made services. These services may result in the calculation of specific parameters outside the standards or to a facilitation of the use of the data. They are designed to optimize data recovery times or to adapt format. This regular or one-off ocean information is delivered for a specific area at the right time, in the right format.
Here some tailor-made services for our shareholders and associated entities, accompanied by a user testimonial.
Maritime Safety: Operational drift model of Meteo France, as part of its contribution to the fight against accidental pollution and to maritime search and rescue
Marine Resources: Processes responsible for the proliferation of invasive brown algae, the "sargasses", supported by IRD&CNRS- Coral mapping and bleaching process within the framework of TARA Coral Odyssey supported by the CNRS
Weather, Climate and Seasonal forecasting: Tropical cyclone forecasting of Meteo France- Valorization of observations within the framework of “Survostral” , supported by IRD and CNRS- Support to the IRD within the framework of the E.U. project. PREFACE whose main objective is to improve the understanding of climate variability in the Tropical Atlantic
Coastal and Marine Environment: Support to the CNRS for CASSIS-Malvinas project to improve the understanding of the dynamics of the Falklands current- Support to IRD and CNRS for NEMO-GLAZUR64 configuration for medium and small scale modelling studies- Support to the CNRS for “Tidal downscaling from the open ocean to the coast: a new approach applied to the Bay of Biscay”
Evaluation of the Interannual Variability in Stochastic Maps of Potential Oil Leakages within Exploratory Offshore Areas in the Equatorial Margin of Brazil
Santi Coimbra De Oliveira, André Luis;
Montenegro Cabral, Marcelo;
Ferreira Garção, Henery;
De Castro Pellegrini, Júlio Augusto - Prooceano, Brazil
The present work intends to evaluate how the interannual variability may affect oil dispersion stochastic maps obtained with computational modeling. These maps are obtained by the combination by numerous possible trajectories of oil leakages that may be originated from multiple positions within oil and gas offshore exploratory blocks in the equatorial margin of Brazil, more specifically in Pará-Maranhão basin. This effort is part of a R&D project called Costa Norte (in English, North Coast) started in 2016 and funded by Queiroz Galvão Exploração & Produção that aims to develop methodologies to evaluate the vulnerability of the mangrove forests of the equatorial margin of Brazil. The project counts on several research modules (such as oceanographic data acquisition, remote sensing, phytosociological surveying, and computational modeling) and several institutions involved, from both academy (UERJ/UFRJ/UFPA) and the business community (PROOCEANO).
As part of the numerical modeling module of the project, a computational tool and a methodology were developed for a preliminary mapping of areas potentially affected by oil leaks that may occur anywhere within the area of the blocks acquired during the last ANP (Brazilian National Petroleum Agency) bid rounds. During the environmental permitting processes for oil exploration and production activities in Brazil, usually, sophisticated three-dimensional lagrangian models are used, which make it impossible to simulate very wide periods or a large number of spill positions. The new methodology simplifies the modeling, such as removing weathering processes, making it computationally feasible while maintaining the conservatism required for oil modeling. Through this, it was possible to perform oil stochastic drift simulations over many years of environmental data and considering hundreds of origins for the oil slicks. Each new 30-days simulation was initiated every 2 days and the oil leak positions are spaced by 10 km. As environmental data, 10 years (2007 - 2016) of currents obtained from an eddy‐resolving regional hindcast simulation and winds obtained from global reanalysis were used. The results evaluated in this work are composed of a total of 215,350 oil drift simulations.
The 10 years of results allowed the evaluation of the interannual variability in the probability maps. Deviation maps of each year were made in relation to the average, as well as histograms that allowed quantifying the variability in percentage terms. The greatest difference from the average was observed in the 2016 map, where 99% of the grid points presented values with deviations below 8.6% of oil presence probability. It has been noted that the differences can occur both in offshore and near-coastal regions. The mean positions of the Intertropical Convergence Zone (ITCZ) and the nucleus of the Northern Brazil Retroflection were also considered to evaluate the annual differences.
12:10 - 12:30
12:30 - 13:30
13:30 - 15:15
13:30 -
Applications of and Requirements for Using Physical Velocity Fields When Studying Ocean Biogeochemistry and Ecosystem Dynamics
Jonsson, Bror Fredrik (1);
Salisbury, Joe (2);
Clayton, Sophie (3) - 1: Plymouth marine laboratory, United Kingdom;
2: University of New Hampshire;
3: Old Dominion University
While it is abundantly clear that pelagic ecosystems closely interplay with the surrounding physical environment, it is less obvious how such interactions should be assessed and modeled. There are significant challenges to address the present ability of processes studies and observation and how to best bridge the varying temporal and spatial scales of interest.
In this presentation we show some examples of how these questions can be addressed by using physical velocity fields such as AVISO/Oscar together with other remotely sensed products. We present work is where Lagrangian particle tracking act as a unifying framework to provide comprehensive statistics, and we discuss the necessary requirements when using physical velocity fields in this fashion.
13:45 -
Testing Ocean Circulation Products With An Ecosystem Model And Biological And Fisheries Data
Lehodey, Patrick (1);
Conchon, Anna (2);
Titaud, Olivier (1);
Senina, Inna (1) - 1: Collecte Localisation Satellite, France;
2: Mercator Ocean, France
An oceanic ecosystem model is presented that includes a representation of low and mid trophic levels (LMTL), i.e., zooplankton and micronekton, and detailed spatial dynamics of exploited fish stocks (e.g. tunas) feeding on these components of the foodweb. Surface and deep (mesopelagic) micronekton are also prey of many marine protected species (e.g. turtles, seabirds, marine mammals) for which very large datasets of satellilte tracked movements become available. The ecosystem model is driven by ocean circulation and temperature products from coarse (1° x month) to high resolution (1/12°d) between surface and 1000m depth, and thus sensitive to this forcing. Accurate observed tracks of micronekton predators and basin scale distributions of fish and catch predicted with a robust Maximum Likelihood Estimation approach using hundreds of thousands of observations illustrate this sensitivity while they provide in the same time a useful feedback to physical oceanographers to identify key issues in their model outputs.
14:00 -
Perspectives and Future Requirements of Lagrangian Altimetry for Ecological and Environmental Studies
d'Ovidio, Francesco;
Baudena, Alberto;
Fifani, Gina;
Cotté, Cédric;
Ser-Giacomi, Enrico;
Sergi, Sara - Sorbonne Universités, LOCEAN-IPSL, France
The Lagrangian approach is based on the analysis of particle trajectories advected in a fluid. In the case of altimetry, this approach can be employed by integrating numerically the surface currents and by creating in this way a set of trajectories of virtual surface drifters. Statistical information about horizontal transport - like for instance the location and intensity of fronts and transport barriers or the connectivity among different sites - can then be derived. This transport information is gaining more and more interest in ecological and environmental studies, including the interpretation of behavior for marine megafauna, the identification of profitable fishing grounds, or the menaging of contaminant spills. One special attracting advantage of Lagrangian methods is that they mimic the horizontal stirring process induced by the mesoscale currents, and therefore are able to predict part of the filamentation which any advected tracer undergo. Therefore, they represent a way to downscaling altimetry information, finding subgrid transport features. However, the position of the filaments predicted by Lagrangian methods, inherits any spatial error already present in altimetry-derived current maps. This is a serious issue because sometimes altimetry error are of the same order of magnitude of the filament widths. Here we critically these issues looking at some specific case studies, and discussing the future requirements which are expected for Lagrangian altimetry in ecological and environmental applications.
14:15 -
The Large Impact of the Small Scales: How Submesoscale Features Determine the Global Distribution of Microplastic Litter and Other Floating Material
van Sebille, Erik - Utrecht University
The ocean is in constant motion, with water circulating within and flowing between basins. As the water moves around, it carries heat and nutrients, as well as larger objects like planktonic organisms and marine plastic litter around the global oceans. These ocean currents therefore play an important role in the connectivity of marine ecosystems and the transport of environmental pollutants, with the combination of the two associated with the increased pressure of invasive species through high amounts of floating material in the form of plastic debris.
The most natural way to study the pathways of water and the connections between ocean basins is using particle trajectories. This is the Lagrangian Ocean Analysis framework, where virtual particle trajectories are computed by integrating velocity fields from Ocean General Circulation Models (OGCMs).
The power of Lagrangian ocean analysis depends critically on the skill of the underlying OGCM fields. Not only is it important that mesoscale eddies are properly resolved, it was recently shown that even small-scale features such as Stokes drift can have large impact on the global distribution of drifting material such as kelp. Hence, a next frontier for large-scale ocean circulation data sets is the better representation of these submesoscale features; if not their full 3D structure then at least the statistics of them.
In this presentation, I will share some recent results on the Lagrangian simulations of floating material such as microplastic and kelp. I will highlight how combining OGCM data and contemporary and future satellite missions including SKIM, one of two ESA EE9 candidate missions, would improve our ability to simulate the pathways and connectivity of this floating material.
14:30 -
Pathways and Impacts of Marine Debris From the 2011 Tsunami in Japan, Studied Through Synthesis of Numerical Modeling and Data Analysis.
Maximenko, Nikolai A. (1);
Hafner, Jan (1);
Kamachi, Masafumi (2);
MacFadyen, Amy (3);
Murray, Cathryn Clarke (4) - 1: IPRC, University of Hawaii, United States of America;
2: Japan Agency for Marine-Earth Science and Technology, Japan;
3: National Oceanic and Atmospheric Administration, United States of America;
4: Fisheries and Oceans Canada
March 11, 2011 tsunami devastated the east coast of Japan and produced millions of tons of marine debris that drifted across the North Pacific. The extraordinary amount and unusual composition of tsunami debris allowed to document its drift in the ocean and its arrivals on remote shores and helped to better understand the pathways of floating marine debris. A suite of ocean models synthesized with these observations produced most complete description of the debris dynamics, pathways, and fate. In this study, observations were used to prescribe realistic distribution of sources and to optimize model parameters, describing debris interaction with the wind. In return, the models filled large gaps in sparse observations and produced estimates of the integral budgets. For example, the study suggests that the original number of boats lost to the tsunami was about 1,000 and tens of these boats may be still floating in the ocean.
Detailed analysis of model fluxes on the US/Canada West Coast and their comparison with reports of tsunami boats from the same region revealed serious difficulties that even best OGCMs (Ocean General Circulation Models), such as the HYCOM (Hybrid Coordinate Model, operated by the US Navy and used for coordination of such operational activity as oil spill response), experience serious problems with reproducing the timeline of observations. The best correspondence was achieved with a diagnostic model SCUD, whose coefficients are determined by historical data of satellite altimetry, scatterometry and trajectories of Lagrangian drifters. This model successfully reproduced all main peaks of tsunami debris arrival in North America.
Hundreds of aliens species, documented in North America and in Hawaii, suggest that marine debris is not only a kind of pollution and a threat to navigation but also a vector for biological transport and dispersal. Analysis of oceanographic data revealed that the large seasonal cycle characteristic for the area in the eastern Japan, affected by the tsunami, permits survival of Japanese coastal species practically everywhere along the west coast of the USA and Canada. In addition, warm-water species picked by the debris on the southern flank of the Kuroshio Extension front and found alive in Hawaii, carry a risk of invasion to these tropical islands. Numerical experiments confirm the possibility of the alien species survival along the simulated paths of the tsunami debris.
In this presentation we discuss numerical methods available to study the drift of marine debris (particles versus tracer), to calibrate/validate models using sparse observational data and to maximize the utility of satellite and model products in various applications.
14:45 -
Importance of Surface Current Measurements in the Equatorial Belt for the Understanding of Ocean and Climate Dynamics with Focus on the Atlantic Ocean
Brandt, Peter - GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
The ocean surface current is an essential ocean and climate variable defining tropical ocean dynamics and air-sea interaction including processes such as equatorial waves, tropical instabilities as well as heat and freshwater advection, entrainment and mixing contributing to the mixed layer budgets. The mixed layer heat budget represents the basis for the understanding of tropical SST variability and the causes of the still severe biases in climate models. Near the equator, there is a strong imbalance between the tendency of mixed layer heat storage and the atmospheric heat fluxes. Here, ocean dynamics plays a crucial role in closing the budget. The quantification of the budget terms requires information on surface currents. Up to now, velocity data used for seasonal budget calculations is based on spatially distributed surface drifters and surface drifts from Argo floats as well as on velocity observations at few moored buoys. However, error estimates from the limited number of data are quite substantial indicating the inappropriateness of combined drifter and float data to address interannual variability or long-term changes of terms within the heat and freshwater budgets. The horizontal resolution of moored velocity observations performed at the tropical buoy array do not resolve the near-equatorial current bands and mesoscale variability including tropical instability waves. Moreover velocity products derived from sea level anomaly and surface winds often fail in the equatorial belt because of the inappropriateness of the geostrophic approximation due to the importance of time derivatives and nonlinearities. We will review and discuss the limitations of the current observing system for the surface velocity and the improvements that would emerge from the availability of continuous remotely sensed surface velocities for the analysis of near-equatorial ocean and climate dynamics.
15:00 -
Constraining The Momentum Transfer in Ice Covered Oceans: Winds, Waves, Sea Ice Drift, and Surface Currents with EE9 Satellite Mission SKIM.
Tsamados, Michel;
Heorton, Harry - CPOM, Earth Sciences, UCL, United Kingdom
The drift of sea ice upon the polar oceans is a result of the balance between quadratic surface stresses at the air and ocean interfaces, the Coriolis acceleration, sea surface tilt and internal ice stresses. For ice concentrations less than 95% internal ice stresses are small and sea ice is said to be in 'free drift'. In this work we consider data from individual drifting buoys as well as Arctic wide gridded fields of wind, sea ice and ocean velocity to invert the momentum equation and estimate the associated quadratic drag parameters and therefore constrain the momentum budget in the ice covered seas.
In ice-covered regions the interface between atmosphere and ocean differs from its open ocean counterpart in many ways: the surface topography in contrast to the waves in the open ocean appears as frozen on time and length scales spanned normally by the wave spectra; the ice cover acts as an additional insulating layer both thermodynamically due to the low conductivity of ice and snow and mechanically due to the rigidity of ice floes; the sea ice seasonal evolution drives a buoyancy forcing at the ocean surface both via its energy (wind forcing, heat fluxes) and salinity modulation (brine release, freezing); the sea ice modifies turbulent fluxes of momentum, heat, freshwater, humidity, gas, and other tracers via due to its complex surface topography and two-phase nature with alternating open ocean (leads in the pack ice or of open ocean in the Marginal ice zone (MIZ)) and ice features (floes).
The state of the sea ice is controlled by an interplay of dynamics and thermodynamics on all spatiotemporal scales represented by a myriad of processes such as ice growth and melt, mechanical strength of the ice, ridging, sea ice wave interactions, fast ice or leads formation. An observational gap remains at short time and length scales to resolve those faster processes. Over synoptic and slower time scales, the wind and ocean forcings, together with the internal forces in the sea ice control the sea ice motion and ultimately the total and regional ice volume contained in the polar oceans via redistribution of ice and export mostly out of the Fram Strait in the Arctic or via Ekman transport to the warmer Southern latitudes in the Antarctic.
With the advent of polar oceanography from altimeters in ice-covered regions, important new questions can now be addressed regarding the freshwater fluxes, surface currents and Eddy kinetic energy, as well as the spinning up or down of polar gyres. To improve further upon the resolution probed by conventional altimetry requires the joint measurements of surface winds, ice drift and ocean currents at sub-synoptic and Eddy resolving length scales that SKIM can achieve.
15:15 - 15:45
15:45 - 16:15
Improving observations in the Agulhas Current through the Gliders in the Agulhas (GINA) initiative
Krug, Marjolaine (1,2,3);
Swart, Sebastiaan (4);
Maja, Tumelo (2,3) - 1: Council for Scientific and Industrial Research (CSIR), Natural Resources and the Environment, Cape Town, South Africa;
2: Department of Oceanography, University of Cape Town (UCT), South Africa;
3: Nansen-Tutu Centre for Marine Environmental Research, Department of Oceanography, University of Cape Town, South Africa;
4: University of Gothenburg, Department of Marine Science
The Agulhas Current is an intense and narrow flow associated with surface velocities often in excess of 4 knots. The Agulhas Current flows in close proximity to the shore and therefore slight changes in its direction or strength directly impact coastal and shelf regions. Our understanding of how the Agulhas Current influences our coastal regions is limited. This is partly because changes in ocean circulation between the Agulhas Current and the coast often occur over short space and time scales which are difficult to observe and predict. The 1st glider experiment in the Agulhas Current region, the Shelf Agulhas Glider Experiment (SAGE, http://socco.org.za/sage/), proved that depth-profiling gliders could be used to observe and characterise fine scale ocean processes at the Aguhas Current’s inshore front. Following the success of SAGE and in light of a growing regional interest, the multi-institutional Gliders in the Agulhas (GINA) scientific consortium was established. Several glider deployments have already occured as part of GINA, in August / October 2017 and September / October 2018 with another deployment planned in February / March 2019. The increased number of surface and underwater observations from the gliders presents an opportunity to validate and improve satellite remote sensing products in the regions as well as increase our understanding of the Agulhas Current's variability. Here we present some of the benefits of establishing a sustained glider observing networtk in the region. Some preliminary analyses of glider observations collected in a large Agulhas Current meander (Natal Pulse) show that the information collected from gliders can significantly improve our portrayal of mesoscale processes from satellites.
Seasonal, Interannual and Decadal Variability of the Sicily Channel Dynamics
Menna, Milena (1);
Poulain, Pierre-Marie (1,2);
Ciani, Daniele (3);
Doglioli, Andrea (4);
Rio, Marie-Helene (5);
Notarstefano, Giulio (1);
Gerin, Riccardo (1);
Santoleri, Rosalia (3);
Gauci, Adam (6);
Drago, Aldo (6) - 1: OGS, Italy;
2: CMRE, Italy;
3: ISMAR, CNR, Italy;
4: MIO, France;
5: ESA-ESRIN, Italy;
6: Physical Oceanography Research Group, Malta
The dynamics of the Sicily Channel is highly influenced by the seasonal variability of the Mediterranean basin-wide circulation, by the interannual variability of the numerous mesoscale structures present in the Channel, and by the decadal variability of the adjacent Ionian Sea. In the present study, all these aspects are investigated using in-situ (Lagrangian drifter trajectories and float profiles) and satellite data (Absolute Dynamic Topography, Sea Level Anomaly and Sea Surface Temperature). Drifter and altimeter data are used to describe the seasonal and decadal variations of the surface currents. Results allow adding further insights on the circulation patterns already described by previous studies, such as the double bifurcation of the Atlantic Tunisian Current and the seasonal variability of the Sirte Gyre. The main mesoscale structures of the Sicily Channel have been identified over the years by numerous works with particular focus on eddies locations and sense of rotations, but their temporal variability and, in some cases, their formation mechanisms are still unknown. In this context, the present work aims to deepen the knowledge on the mesoscale field using ‘optimal currents’ derived from the merging of the satellite Sea Level Anomaly and Sea Surface Temperature data fields. These multi-sensor currents not only improve the present-day altimeter-derived geostrophic currents, but also retrieve the ageostrophic component of the circulation field. The high spatial and temporal resolution of the ‘optimal currents’ are unique to decipher in detail the interannual variability of the main, quasi-permanent mesoscale structures. The vertical structures and the hydrological characteristics of these mesoscale eddies are delineated using Argo float profiles.
Evaluation of the GlobCurrent Ocean Surface Current Products in Australia
Cancet, Mathilde (1);
Griffin, David (2);
Cahill, Madeleine (2);
Chapron, Bertrand (3);
Johannessen, Johnny (4);
Donlon, Craig (5) - 1: NOVELTIS, France;
2: CSIRO, Australia;
3: IFREMER, France;
4: NERSC, Norway;
5: ESA/ESTEC, The Netherlands
Today, the global ocean surface current products (GlobCurrent, OSCAR, AVISO, CTOH…) are mainly based on the geostrophic and the Ekman contributions derived from altimetry and wind observations, respectively. The higher frequency processes, such as the ocean tides, are not included in these products, although they often represent one of the main contributors to the ocean currents on the shelves.
Australia’s marginal seas include a wide range of ocean current regimes ranging from tide-dominated in the North-West where the continental shelf is wide, to boundary current- and eddy-dominated in the South-East, where the shelf is narrow. Here, we take the opportunity to test the GlobCurrent surface ocean current products against in-situ observations in these two contrasting regimes. Observations by Acoustic Doppler Current Profiler (ADCP) instruments of Australia’s Integrated Marine Observing System (IMOS) and drifting buoys of the Global Drifter Programme (GDP) are used.
The monthly-timescale variability of the GlobCurrent alongshore current component is in moderately good agreement with the observations on the continental shelf in the South-East but neither the shorter period variability nor the long-term mean are representative of the ADCP observations. The error of the time-mean velocity, derived from the Mean Dynamic Topography (MDT) CNES-CLS13, is the dominant error because that product is not designed to represent the highly anisotropic nature of the sea level gradients over the continental shelf nor the constraints on the flow field that are imposed by the topography. While the observed tidal currents are negligibly small, the wind-driven signals are not, but these are too transient to be adequately sampled by altimetry. The inclusion of an Ekman component does not represent these signals because the interaction of the Ekman transport with the coastal boundary condition is not included. We thus conclude that the GlobCurrent product needs improvements before it can be described as very suitable for applications on this narrow continental shelf. Off the continental shelf, in contrast, the GlobCurrent products compare quite well with the trajectories of drifting buoys, confirming that the products are quite suitable for blue-water applications.
In contrast to the South-East, the tides are very strong in the North-West region of Australia. The sub-tidal variability is weak, in both relative and absolute senses. Consequently, the removal of the tidal signal from the sea level observations needs to be very complete for the residual error to be smaller than the true sub-tidal signal. Transient wind forced signals are also occasionally large so this step of the de-aliasing also needs to be very accurate. Unfortunately, it appears that more work is required before accurate estimates of sub-tidal variability are available from GlobCurrent: the magnitude of the GlobCurrent estimates of sub-tidal current variability far exceed the magnitude of, and are uncorrelated with, the detided ADCP data.
Developing Multi-Satellite Ocean State Products For The Marine Resources Management: Results From The OSMOSIS Project
Guinehut, Stephanie (1);
Rio, Marie-Helene (3);
Buongiorno-Nardelli, Bruno (2);
Lehodey, Patrick (1);
Matthieu, Pierre-Philippe (3);
Mulet, Sandrine (1);
Santoleri, Rosalia (2);
Senina, Inna (1);
Stum, Jacques (1) - 1: CLS, France;
2: ISAC-CNR, Italy;
3: ESA, Italy
Micronekton organisms are both the prey of large ocean predators, and themselves also predators of eggs and larvae of many species from which most fishes. The micronekton biomass concentration is therefore a key explanatory variable that is usually missing in ecosystem models to understand individual behaviour and population dynamics of large oceanic predatorsthat are either targeted by fisheries (tuna, swordfish, marlin, etc.) or strictly controlled in by-catch (bluefin tuna, sharks), or fully protected (marine turtles, seabirds, marine mammals).
In that context, the OSMOSIS (Ocean ecoSystem Modelling based on Observations from Satellite and In-Situ data) project aims at demonstrating the feasability and prototyping an integrated system going from the synergetic use of many different variables (Sea level, Earth Marine geoid, Sea Surface Salinity, Sea Surface Temperature, Ocean color) measured from space to the modeling of the distribution of micronekton organisms. In this paper, we present how data from CRYOSAT, GOCE, SMOS, ENVISAT, together with other non-ESA satellites and in-situ data, can be merged to provide the required key variables needed as input of the micronekton model: the 3D description of the ocean state (Temperature, Salinity, Currents), the Primary Production and the Euphotic Depth. Also, micronekton density maps obtained in the Southern Indian and Pacific Ocean by forcing the model with the OSMOSIS input fields are presented and discussed.
Geostrophic Currents in Polar Oceans - Combining Satellite Altimetry Measurements with Model Simulations
Müller, Felix Lucian;
Passaro, Marcello;
Dettmering, Denise;
Seitz, Florian - Deutsches Geodätisches Forschungsinstitut der Technischen Universität München (DGFI-TUM), Germany
Satellite altimetry has been providing valuable information about the sea surface and its temporal variations for more than 25 years. When combined with gravity models, information about mean and absolute dynamic ocean topography (DOT) can be derived – a quantity used to compute geostrophic currents and to study ocean mass and heat transport as well as major ocean flow pathways, current velocities and directions.
Polar regions, especially the Arctic Ocean are among the regions on Earth that are most affected by climate change. Increasing temperatures and melting glaciers produce an enhanced fresh water inflow to the polar oceans, capable of evoking significant changes in the global ocean circulation system. Particularly in these areas, satellite altimetry observations are affected by seasonally changing sea-ice coverage and difficult ocean conditions leading to a fragmentary data sampling and reduced data reliability.
In order to overcome this problem, an ocean model considering major sea-ice drift patterns is used to fill data gaps with the aim to obtain a homogeneous DOT representation. For this purpose, the Finite Element Sea ice-Ocean Model (FESOM) is used. It provides daily water elevations with high spatial resolution. The combination is based on the spatially homogeneous information of the model and the high temporal resolution of 25 years of altimetry. Derived DOT heights enable consistent investigations of ocean surface current changes.
This contribution will address:
Recent progress in satellite altimeter data pre-processing in polar areas (water/ice classification, range retracking) as well as existing limitations and challenges.
A comparison of modeled and observed DOT representations in the Greenland Sea, focusing on the identification of advantages and limitations of both quantities.
A description of an innovative combination approach to make use of the advantages of observations and models of polar sea level variability.
A quality assessment of the combined products based on a comparison with geostrophic velocities from surface drifters.
Ideas for possible improvements of both the data basis and the combination approach as well as an outlook on possible applications.
Needs in near-surface currents observations in the Equatorial and Tropical Pacific Ocean
Cravatte, Sophie E. (1);
Ardhuin, Fabrice (4);
Brandt, Peter (5);
Maes, Christophe (2);
Marin, Frederic (1);
Renault, Lionel (1);
Reverdin, Gilles (3) - 1: IRD, LEGOS, France;
2: IRD, LOPS, IUEM, Brest, France;
3: CNRS, LOCEAN, Paris, France;
4: CNRS, LOPS, IUEM, Brest, France;
5: GEOMAR, Germany
Our knowledge of the near-surface currents (in the upper tens of meters) is based on existing in situ observation networks measuring currents directly (including the Global Drifter Program, Argo, Shipboard-ADCP, the tropical moored arrays), and on products indirectly derived from satellite observations of sea surface height and ocean vector winds. In the equatorial regions, these datasets have serious limitations: in situ observations have a limited spatial, depth and temporal coverage. The central and eastern equatorial regions in particular are poorly sampled by surface drifters because of equatorial Ekman divergence. There are also large uncertainties in satellite products within about 5° of the equator.
Our understanding of equatorial dynamics is thus limited by a lack of observations. The upper few tens of meters contain the mixed layer diurnal jet, essential for understanding the penetration of surface momentum into the ocean, in combination with deeper current measurements. Moreover the mixed layer depth in upwelling regions is often less than 15 m corresponding to the drift depth of surface drifters resulting in a mismatch between mixed layer and drifter velocities. A lack of resolution of the velocity shear in the near-surface layer prevents us from fully understanding the response of mixed-layer-surface currents to winds, and the resulting feedbacks on the atmosphere. This depth range also contains most of the equatorial divergence, important for understanding the equatorial upwelling zonal and meridional structure, and its temporal variability. Surface currents are also needed for better constraining the cold tongue heat budget (horizontal advection, upwelling and mixing) playing an important role for ENSO diagnostics and prediction.
The existing observations do not allow either to monitor frontal areas with small spatial scales, which are key regions for air-sea interactions, and targets for the future TPOS. In the central Pacific, the eastern edge of the Warm Pool is a key feature for ENSO prediction; characterized by a frontal zone and a zonal convergence of currents, and its displacements at high and low frequency would be better tracked by surface currents direct observations. North of the cold tongue, a frontal zone separating the cold waters at the equator from warmer waters north of it is modulated by tropical instability waves (TIWs) with strong surface zonal and meridional velocity variability, with impacts on the equatorial heat budget. Near the Marquesas archipelago, TIWs also play a crucial role on the so-called island mass effect and impact the local biogeochemistry and biology conditions.
This talk will review our knowledge about the variability of near-surface currents in the tropical Pacific Oceans. It will discuss the limits and strengths of the existing observations, the key questions that remain open concerning the spatial and temporal variability of these currents, and what we know about the structure of near-surface shear in the ocean. It will discuss the requirements in terms of temporal and spatial resolution to resolve the varying current structures, including sharp gradients and the diurnal cycle.
Near-surface current shear from in situ measurements in the Tropical Atlantic and Pacific Oceans.
Reverdin, Gilles (1);
Herbert, Gaelle (2);
Cravatte, Sophie (3);
Habasque, Jérémie (4);
Bourlès, Bernard (5) - 1: CNRS, LOCEAN, Paris, France;
2: IFREMER, LOPS, Brest, France;
3: LEGOS, IRD/UPS/CNRS, Toulouse, France;
4: IRD, LEMAR, Brest, France;
5: IRD, IMAGO, Brest, France
The surface circulation has been explored from existing in-situ observation networks in the equatorial Atlantic and Pacific Oceans (including the Global Drifter Program, Argo, and the PIRATA-TAO-TRITON buoys array). The mean seasonal cycle of large scale surface zonal currents is resolved by these networks, despite equatorial divergence and upwellings affecting near surface drifting devices. Thus comparing them also provides information on the large near-surface shear between 1m and 15m depths. This shear-component is found to be large and contributing a significant share of the seasonal cycle portrayed. The shear is investigated to assess the relative importance of different contributions: surface wind stress, near-surface stratification, and geostrophic shear. This is in particular considered in the Atlantic Ocean which presents more regularity in its seasonal cycle and less interannual variability, but the results can be extrapolated to the Pacific Ocean, although interannual variability linked in particular with ENSO needs to be considered. We will also review process-study investigations with highly vertically resolved moored observations both in the tropical Atlantic (TACOS at 4°N/23°W) than in the equatorial Pacific Ocean.
The existing observations do not allow to monitor frontal areas with small spatial scales, which are key regions for air-sea interactions, and might present different shear structures. There is also insufficient observations to tackle interannual variability at the required detailed level.
Combining GlobCurrent Ocean Current Products with Tidal Currents to Monitor Marine Litter in the North Atlantic Ocean
Lux, Muriel;
Sahuc, Etienne;
Cancet, Mathilde;
Denisselle, Matthieu - NOVELTIS, France
With an increasing rate of production, plastic management has become a global concern. As a majority of plastic items are single use products, mismanagement of waste leads to a lot of items ending up at sea. Thus, plastic litter monitoring have become of great importance in the aim of the ocean and water quality protection. The IFADO (Innovation in the Framework of the Atlantic Deep Ocean) project aims to create new marine services to support the Marine Strategy Framework Directive implementation with the North Atlantic Ocean as a study case. One of the objectives of this project is to use Earth Observation products in order to characterize marine litter accumulation in the North Atlantic Ocean.
The GlobCurrent ocean surface current products are used in this study. These products consist in geostrophic and Ekman contributions derived from altimetry and wind observations, respectively. These products do not include ocean tides, even though they are a major contributor to the ocean currents on the continental shelves and in the coastal regions. As about 80% of marine litter originates from land-based sources, coastal currents have an essential role on these debris pathways, in particular for stranding. Hence, NOVELTIS used its own tidal atlas to add the surface tidal current component to the GlobCurrent data and implement a more realistic surface ocean current product. As current tidal atlases only provide the barotropic component of ocean current, NOVELTIS has developed a methodology based on maritime industry guidelines to compute the surface tidal current to be added to the GlobCurrent ocean surface current products.
This study presents an assessment of the GlobCurrent products (original and with tidal currents) against drifting NOAA buoys in the Bay of Biscay. A skill score has been implemented to assess the improvement of ocean current products when the tidal component is added. Then, these surface ocean currents products were used as input of a Lagrangian modelling tool (Opendrift) in order to highlight plastic particles convergence zones, pathways and main stranding areas. Various scenarios were considered to compute the marine litter trajectories with this ocean tides contribution. The results of this study highlight the necessity for global ocean surface current products (such as GlobCurrent) to take into account the tidal current component to improve their representation of the coastal ocean dynamics.
Distributing and Visualizing Drifter Data in COSMO
Ballabrera, Joaquim;
García, Emilio;
Jiménez Madrid, José Antonio;
Pérez, Fernando;
Isern-Fontanet, Jordi - Institut de Ciències del Mar, Spain
In the context of the COSMO project (CTM2016-79474-R,MINECO/FEDER,UE) a series of activities are underway to assess the quality of the ocean currents derived by ocean forecast systems. Key elements for these assessment are a set of regular Lagrangian experiments performed by Spanish Salvamento Marítimo and the release of 18 surface drifters near Gibraltar Strait during MEDGIB-II Campaign on January, 2018.
The surface drifters use various kinds of transmission technologies, different types and formats and come from different data sources. These different formats and data sources need to be unified and standarized. We have opted for the GeoJSON format. We have developped a system that downloads data from all the transmission data source providers, process and convert them to GeoJSON and KML format to be directly vieweb in Earth browsers.
We have also developped an interactive GUI application (COSMO-VIEW) able to remotely access ocean current predictions provided by Puertos del Estado and SOCIB through OPenDAP protocol and to launch MOTU queries to the COPERNICUS service to download data from their operational prediction systems. The tool is able to superpose the latest images of satellite sea surface temperature and the hourly current from the various HF Radar stations provided by Puertos del Estado and SOCIB, as well as to superpose drifter trajectories. The COSMO-VIEW model can also be used as interface to launch the COSMO Lagrangian Models.
Monitoring the Algerian Basin through Glider Observations, Satellite Altimetry and Numerical Simulations during the ABACUS Project
Aulicino, Giuseppe (1);
Cotroneo, Yuri (2);
Ruiz, Simon (3);
Pascual, Ananda (3);
Sanchez Roman, Antonio (3);
Fusco, Giannetta (2);
Torner Tomas, Marc (4);
Budillon, Giorgio (2);
Tintoré, Joaquin (4) - 1: Università Politecnica delle Marche, Italy;
2: Università degli studi di Napoli Parthenope, Italy;
3: Instituto Mediterráneo de Estudios Avanzados, Spain;
4: Balearic Islands Coastal Observing and Forecasting System, Spain
The Algerian Basin is a key component of the general circulation in the Western Mediterranean Sea. The presence of both fresh Atlantic water and more saline Mediterranean water gives the basin an intense inflow/ outflow regime and complex circulation patterns. Energetic mesoscale structures that evolve from meanders of the Algerian Current into isolated cyclonic and anticyclonic eddies dominate the area, with marked repercussions on biological activity. Despite its remarkable importance, this region and its variability are still poorly known and basin-wide knowledge of its meso- and submesoscale features is still incomplete. Studying such complex processes requires a synergistic approach that involves integrated observing systems. In recent years, several studies have demonstrated the advantages of combined use of autonomous underwater vehicles, such as gliders, with a new generation of satellite altimetry. In this context, we present the monitoring activities conducted in the Algerian Basin between September 2014 and May 2018, in the framework of several editions of the “Algerian BAsin Circulation Unmanned Survey - ABACUS” project. These activities were realized through the SOCIB (Balearic Islands Coastal Observing and Forecasting System) Glider Facility Open Access Programme and were supported by the Joint European Research Infrastructure network for Coastal Observatories (JERICO) Trans National Access (TNA), the SOCIB external access and the JERICO-NEXT TNA.
During the ABACUS missions, a total of 12 glider transects were carried out between the island of Mallorca and the Algerian coast, collecting Temperature, Salinity, Turbidity, Oxygen and Chlorophyll concentration high resolution data in the first 975 m of the water column. In situ data collection was supported by near real time remotely sensed data from different platforms over the Western Mediterranean Sea. In particular, gridded altimetry data provided by the Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO), Sea Surface Temperature (SST) and Chlorophyll-a concentration (Chla) information from MODerate resolution Imaging Spectroradiometer (MODIS) data acquired by NASA were used to provide a large scale description of the dynamics and surface water masses. Glider surveys were always conducted along the groundtracks of operating altimetry satellites, i.e. SARAL/AltiKa and Sentinel-3, and were planned in order to get always the glider at sea during the satellites overflight. Furthermore, the adaptive sampling capabilities of the Slocum gliders also allowed to partially modify their tracks in order to investigate the oceanographic characteristics of interesting mesoscale structures identified through altimetry.
Here we report on comparative analyses of glider measurements with both co-located (SARAL/AltiKa and Sentinel-3) altimetric products, and CMEMS numerical simulations. Results show similar patterns for glider-derived dynamic heights and altimetric absolute dynamic topography. Even though larger discrepancies are observed near the Balearic and Algerian coasts, correlation coefficients between glider and satellite observations seem mostly to be affected by synopticity between remote sensed and in situ measurements.
We expect to apply this ocean observing strategy also for validating products provided by new generation altimeters that are designed to be better suited for coastal, mesoscale and submesoscale monitoring, such as the forthcoming wide-swath radar interferometer Surface Water and Ocean Topography (SWOT).
Evaluation of New Air-sea Surface Fluxes Product Of Esa Program (TIE-OHF) And Geostrophic Surface Currents Of GlobCurent Project In The North-western Mediterranean (GULF OF LION)
Ludos-herve, Ayina (1);
Bertrand, Chapron (2);
Piolle, Jean-Francois (2) - 1: Inno'Energy, France;
2: Ifremer, France
The new high-resolution air-sea flux of ESA program TIE-OHF associated for the first time with surface geostrophic currents of the GlobCurent project are exploited with the prospect of the closure of oceanic heat and water budgets. To start with, a diagnostic tool based on the simplified 2D-mixed layer model (MLM) is used to evaluate the ability of these new satellite and merged products to describe the sea surface temperature (SST) balance and its seasonal variability in the North-Western Mediterranean in 2015.
The results of the diagnostic show that the net heat fluxes of the TIE-OHF program still have positive biases leading to the annual warming of the surface temperature in the North-Western Mediterranean. This annual warming trend is largely related to the low latent heat flux compared with the estimates from observations by Caniaux et al (2017). We show also that GlobCurent geostrophic currents correctly restore the circulation of the North-Western Mediterranean and its variability at seasonal scales. Generally, geostrophic advection of temperature tends to warm up the surface temperature. Horizontal and vertical Ekman advections remain the main contributors to cooling the surface temperature in the North-Western of the Mediterranean in 2015.
Dynamical-Statistical Mechanics Approach to Large Scale Ocean Phenomena. El Niño case: Analytical Results for the Probability Density Function and for the recurrence Timing.
Bianucci, Marco (1);
Capotondi, Antonietta (2);
Merlino, Silvia (1);
Mannella, Riccardo (3) - 1: ISMAR - CNR, La Spezia, Italy;
2: University of Colorado, CIRES, Boulder (CO) USA, and NOAA-ESRL, Boulder (CO) USA;
3: Physics Dept. Pisa University
A complex collection of geophysical causes contributes to the emergence of Large Scale Oceanic Phenomena (MOC; NAO, ENSO...). Thus in Geophysical fluid dynamics, important events, like ENSO, can be considered as large time-scale phenomena emerging from the observation of few ocean degrees of freedom of a more complex system, including the interaction with the atmosphere.
In this talk, we show that a revisited Mory-Zwanzig procedure applied to complex Geophysical phenomena, allows us to obtain analytical results for the statistics of the dynamics of large scale events. Namely, we introduce in this field an approach derived from the context of the foundation of Thermodynamics: the role of the “microscopic” system is now played by the atmosphere (and other "unobservable" degrees of freedom), while the Ocean variables play the role of the “macroscopic” system. Thus, as for Thermodynamics, El Niño (for example) emerges as a universal large scale property from a general class of complex systems. After presenting the projection approach adapted to general non Hamiltonian dynamical systems, we apply the results to the ENSO and we obtain the Analytical stationary ProbabilityDensity Function and the analytical Estimate of the average Timing of Strong Events.
References:
Bianucci M., Capotondi A., Merlino S., Mannella R. (2018), Estimate of the average timing for strong El Niño events using the recharge oscillator model with a multiplicative perturbation. Chaos 28(10):103118.
Bianucci M., Capotondi A., Mannella R., Merlino S. (2018), Linear or non Linear modeling for ENSO dynamics? Atmosphere 9(11). doi:10.3390/atmos9110435.
Bianucci, M. (2016), Analytical probability density function for the statistics of the ENSO phenomenon: Asymmetry and power law tail, Geo. Res. Lett. 43(1), 386-394
M. Bianucci. Using some results about the Lie evolution of differential operators to obtain the Fokker-Planck equation for non-Hamiltonian dynamical systems of interest. Journal of Mathematical Physics, 59(5):053303, 2018.
M. Bianucci. Large scale emerging properties from non Hamiltonian complex systems. Entropy, 19(7), 2017.
M. Bianucci and S. Merlino. Non Standard Fluctuation Dissipation Processes in Ocean-Atmosphere Interaction and for General Hamiltonian or Non Hamiltonian Phenomena: Analytical Results. Mathematics Research Developments. Nova Science Publisher, 2017.
M. Bianucci. On the correspondence between a large class of dynamical systems and stochastic processes described by the generalized Fokker Planck equation with state-dependent diffusion and drift coefficients. Journal of Statistical Mechanics: Theory and Experiment, 2015(5):P05016, 2015.
Estimation, Verification and Application of Altimeter-based Ocean Currents Along the Northwestern Atlantic Shelf
Vandemark, Douglas (1);
Feng, Hui (1);
Egido, Alejandro (2);
Jonsson, Bror (3) - 1: Univ. of New Hampshire, United States of America;
2: NOAA – Laboratory for Satellite Altimetry, GST Inc.;
3: Plymouth Marine Laboratory
Satellite altimetry has become a key global platform for monitoring upper ocean surface ocean currents and associated dynamics. As known, traditional satellite altimetry has been built primarily for open ocean application. In the last decade, significant advances using altimetry nearer to the coast have been made including work to refine and apply ocean current estimates using both along-track and gridded data products (Feng et al, 2011,2016, 2018a). Most recently, extensive evaluation of GlobCurrent geostrophic and total surface current estimates using multi-year ADCP and HF radar datasets indicates significant promise for GlobCurrent application for shelf-slope process studies on the Northwestern Atlantic Shelf. Separately, our team has begun regional coastal assessments of satellite currents very near the coast of Nova Scotia as derived using so-called Fully-focused Synthetic Aperture Radar (FF-SAR) processing of Cryosat-2 measurements. This poster will provide an overview and update for these studies where we are now performing shelf-wide GlobCurrent evaluations that include the new beta release MDT (MDT_CNES_CLS18) with an improved resolution (1/8 degree grid) and expanding FF-SAR datasets to include Sentinel-3A/3B measurements.
Ocean Dynamics Scales and Fate of Marine Plastics
Assad, Luiz Paulo de Freitas (1);
Neves, Ramiro (2);
de Pablo, Hilda (2);
Campuzano-Guillén, Francisco (2);
Canelas, Ricardo (2);
Juliano, Manuela (3);
Sepp, Antonio Augusto (4);
Fernandes, Alexandre (5);
Franz, Guilherme (6);
Rollnic, Marcelo (7);
Böck, Carina Stephoni (1);
Landau, Luiz (1);
Moutinho, José (8) - 1: Laboratory of Computational Methods in Engineering – Federal University of Rio de janeiro, Brazil;
2: Maretec-Larsys, Instituto Superior Técnico, University of Lisbon;
3: IMAR, University of Azores;
4: University of Bologna;
5: Oceanography Faculty of Rio de Janeiro State University;
6: Marine Research Centre, Federal University of Paraná;
7: Marine Geophysics Laboratory, Federal University of Pará;
8: AIR Centre
Plastics in the oceans are a major actual environmental problem. Although plastics’ debris are mostly used on land, the quantity reaching the oceans the ultimate destination is most often goes beyond the carrying capacity of the marine ecosystems. Once plastics reach the oceans, their fate is determined by the different scales of ocean dynamics and by the density of the plastics. Land-originated plastics enter in the oceans in coastal areas: the probability of floating plastics to the beach along the coastal line depend on the currents, on wave drift and on the wind. Neutral buoyant plastics are carried by ocean currents mostly in the mixed layer and plastics denser than the water reach the bottom and settle of roll over the bottom according to the local near bottom shear and gravitational forces.
This paper addresses the fate of plastics as a function of their density and of the importance of the ocean circulation scale. Plastics is the near shore are assessed considering continuous emissions from inside estuaries. Using local models, it is analyzed the effect of density, currents, wind and wave drift. the discharged across estuaries are assessed considering plastic density, wind and wave drift using continuous emissions. The dispersion of neutral and floating plastics at regional scale is addressed using a regional circulation model able to simulate the estuarine plumes. Using this model, it is possible to compute the residence time in a coastal region and the transport towards the ocean. The fate of these plastics is determined using instantaneous emissions. Particles are released in the whole ocean and their fate is computed using the global ocean circulation and the plastic floating properties.
A hierarchy of nested models in a downscaling philosophy has been implemented in two areas of the North and South Atlantic, forced externally by the Copernicus global ocean solution and validated using satellite data. Results already available show the importance of all scales and how Large Scale circulation determines the long term accumulation zones. Other important results are related to the interaction of plastic destinations with mesoscale oceanic characteristics such as regional ocean vortices and meanders. Future developments include improvements in the representation of plastic interaction with biota through its effect on debris density.
16:20 - 16:45
16:45 - 18:00
16:45 -
Accuracy of Mercator Ocean Global Ocean Surface Current Forecasts, and Needs for Reference Measurements.
Drévillon, Marie (1);
Régnier, Charly (1);
van Gennip, Simon (1);
Levier, Bruno (1);
Law Chune, Stéphane (1);
Drillet, Yann (1);
Rémy, Elisabeth (1);
Greiner, Eric (2);
Lellouche, Jean-Michel (1);
von Schuckmann, Karina (1);
Le Traon, Pierre-Yves (1,3) - 1: Mercator Ocean International, France;
2: CLS, France;
3: Ifremer, France
Mercator Ocean International is developing and operating a global ocean and sea ice analysis and forecasting system at 1/12° horizontal resolution, producing daily 10-day forecasts for all Essential Ocean Variables, physical and biogeochemical, and sea ice variables. These global forecasts and their initial conditions (weekly analyzes) are delivered as part of the Copernicus Marine Environment Monitoring Service CMEMS, also managed by Mercator Ocean International. In 2019, tidal currents and wave induced currents at global scale are also provided together with the surface current products, improving the accuracy of currents for Lagrangian drift applications, among others. Long retrospective time series of ocean reanalyses are also produced with the same ocean analysis system, and span the altimetric period (1993-now). Based on these time series, ocean state monitoring and reporting activities aim at providing regular synthetic and added value information (Ocean Monitoring Indicators) on the state and long term change of Ocean Essential Variables including surface currents. All products/variables are quality assured and thus verified against in situ and/or remote sensing reference observations when and where available. Ocean surface currents are routinely checked against near surface velocities (15m) deduced from drifting buoys trajectories and against GlobCurrent estimates two products also disseminated by CMEMS. Close to the coast, other devices such as high frequency radar measurements and moored currentmeter measurements give an estimate of the ability of the global ocean forecasting system to capture near coastal variability. This presentation will discuss the summary of the various regional surface currents forecast error estimates at the seasonal timescale. Oceanic pathways within Mercator Ocean surface currents will be illustrated with Lagrangian diagnostics. The ability of ocean reanalyses to reproduce ocean surface currents interannual variability will also be illustrated. Finally, we’ll give an overview of the roadmap of ocean modeling and data assimilation developments planned to improve the surface current forecasts, and stress the importance of improving the existing network of surface currents reference measurements but also for improving the forecast through assimilation of surface current observations.
17:00 -
Assessment of Some New Developments to the Met Office Ocean Forecasting System FOAM Using Comparisons to Ocean Current Data
Lea, Daniel J;
Waters, Jennifer;
King, Robert R;
Martin, Matthew J - Met Office, United Kingdom
FOAM is the Met Office's operational ocean forecasting system. This comprises a range of models from a 1/4 degree global to 1/12 degree regional and shelf seas models at 7 and 1.5 km resolution. The system is made up of the ocean model NEMO (Nucleus for European Modeling of the Ocean) and the NEMOVAR assimilation run in 3D-VAR FGAT mode. The system assimilates profile temperature and salinity, in-situ and satellite swath sea surface temperature, altimeter and sea ice concentration data. NEMOVAR has the capability to assimilate velocity data but this is not used at the moment.
Two main ongoing developments will be investigated. We will assess these by validating against ocean current observations. In addition we assess the overall consistency of the assimilated observations using innovation statistics. First, a new MDT, CNES-CLS18-v0, has been released as a beta version. We show some results of tests of this MDT in FOAM and compare them to runs with the older CNES-CLS13 MDT. Second, an upgrade of the global FOAM system to 1/12 degree is in development. This will be compared to the existing 1/4 degree version.
We will discuss how new types of velocity data may improve such assessments in future for both the global and shelf systems. And we will discuss prospects and likely requirements for assimilating velocity data.
17:15 -
GOFS16: a Global Ocean Forecast System at Eddying Resolution
Masina, Simona (1);
Iovino, Doroteaciro (1);
Cipollone, Andrea (1);
Ciliberti, Stefania (1);
Coppini, Giovanni (1);
Trotta, Francesco (2);
Pinardi, Nadia (2) - 1: Euro-mediterranean Center on Climate Change (CMCC), Italy;
2: Department of Physics and Astronomy, University of Bologna, Italy
An operational system to forecast the state of the global ocean has been developed and implemented at CMCC over the last 5 years, and runs daily since July 2017. The system, known as GLOB16, consists of a global ocean/sea ice configurations at 1/16° horizontal resolution of (∼7km at the equator and ∼3km at high latitudes) with 98 unevenly-spaced vertical levels, that makes it one of the few mesoscale-resolving global operational systems in the world. GOFS16 is based on the NEMO ocean/sea ice modelling framework, an open source community model that the CMCC is both user and developer of. The global NEMO configuration is coupled to a three-dimensional variational data assimilation method to provide daily initialization fields. The system assimilates salinity and temperature profiles, sea surface temperature, along track sea surface height, and sea-ice concentration on a daily basis. The forecast system is forced with 3-hourly momentum, radiation, precipitation fluxes from the operational Global Forecast System (GFS) fields, and it runs operationally once a day to produce a 7-day forecast of the three-dimensional temperature, salinity, velocity fields, and sea-ice properties. An overview of the system is presented together with an extensive assessment of its predictive skills.
This forecast system is also used for several downstream applications, namely regional and coastal downscaling in several regions of the world ocean. Downscaling is realized with a new tool, the Structured and Unstructured Relocatable ocean model for Forecasting (SURF) based on NEMO, reaching resolutions of 1/64° and nested within the global operational model. SURF produces forecasts every day with best initial and boundary conditions from GOFS16. An overview of the system is presented.
17:30 -
Data Assimilation for the Reconstruction of High Resolution Ocean Surface properties
Metref, Sammy (1);
Cosme, Emmanuel (1);
Le Sommer, Julien (1);
Verron, Jacques (1);
Brankart, Jean-Michel (1);
Brasseur, Pierre (1);
Tissier, Ann-Sophie (1);
Duran, Marina (2) - 1: Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, France;
2: Laboratoire d'Aérologie, Toulouse, France
New satellite missions will soon provide new types of information on upper ocean circulation (e.g. wide-swath altimetry, surface currents). In combination with existing data, these new missions will offer an unprecedented opportunity to estimate upper ocean circulation from global scale down to submesoscales. But this estimation problem can be expected to be challenging because of: (i) the complex dynamical relations between oceanic variables at fine scales (<100km); (ii) the complex nature of observations (multisensor, irregular sampling in both space and time), and (iii) the specific error budget of each type of observations. Formulating this inverse problem will therefore most likely require the use of advanced inversion methods which adequately take into account the nature of the observations, their distribution and uncertainties, as well as ocean dynamics.
In this presentation, we will review recent advances made in our group on the reconstruction of ocean surface properties at high-resolution from satellite observations. Emphasis will be put on: (i) the assimilation of SST and ocean color images to reconstruct surface currents; (ii) multi-scale data assimilation of nadir altimetry; and (iii) the processing of the errors affecting the future SWOT wide-swath altimeter data. Through these illustrations, we will show the relevance of advanced data assimilation techniques for the reconstruction of high-resolution ocean properties and discuss the possible extensions of these techniques for the estimation of upper ocean circulation in the future.
17:45 -
Ocean Circulation Prediction From Regional to Coastal Scales
Staneva, Joanna;
Schulz-Stellenfleth, Johannes;
Ricker, Marcel;
Grayek, Sebastian;
Jacob, Benjamin;
Stanev, Emil - Helmholz Zentrum Geesthacht, Germany
This work describes recent developments based on advances in coastal ocean forecasting in the fields of numerical modelling, data assimilation, and observational array design, exemplified by the Coastal Observing System for the North and Arctic Seas (COSYNA). The region of interest is the North and Baltic seas, and most of the coastal examples are for the German Bight. Applications are presented to demonstrate the outcome of using the best available science in improved ocean circulation predictions. The applications also address the nonlinear behavior of the coastal ocean, which for the studied region is manifested by the tidal distortion and generation of shallow-water tides. Led by the motivation to maximize the benefits of the observations, this study focuses on the integration of observations and modelling using advanced statistical methods. The role of wave-current interaction processes on ocean circulation and drift model simulations is further investigated with the Geestacht Coupled cOAstal model SysTem GCOAST. We demonstrate that the wave -induced Stokes Coriolis force leads to a deflection of the current. During extreme events the Stokes velocity is comparable in magnitude to the current velocity. The resulting wave -induced drift is crucial for the transport of particles in the upper ocean. Illustrations from the assimilation of remote sensing, in situ and high-frequency (HF) radar data, the prediction of wind waves and storm surges, and possible applications to search and rescue operations are also presented.
18:00 - 18:05
Validation and Error Analysis of a Global Ocean Eddying Forecasting System at 1/16°
Cipollone, Andrea (1);
Masina, Simona (1,2);
Iovino, Doroteaciro (1);
Ciliberti, Stefania (1) - 1: Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC), Italy;
2: Istituto Nazionale di Geologia e Vulcanologia (INGV), Italy
It has been long realized that mesoscale turbulence mostly dominates the ocean circulation on a weekly time basis. While the long time-mean components of oceanic flow have been well documented, its day-by-day variability is still largely unknown. Such puzzle is still unconstrained, despite the constant increase in the number of observations freely accessible year by year.
GOFS16, Global Ocean Forecasting System with a working resolution of 1/16 degree, addresses two key problems: how to model the natural processes at the meso-scale level and what is the best estimation of the current state of the ocean based on observations. A NEMO-LIM2 ocean-sea ice model at 1/16 resolution is employed to solve the hydrostatic, primitive equation of ocean general circulation through a finite difference scheme, a free sea surface and a non-linear equation of state. This is coupled with a 3dvar assimilation system (OceanVar) that is able to ingest multiple and heterogeneous data sources, from in-situ profile, to along-track satellite SLA and SST data, exploiting the same resolution of the model. The system is designed for short-term predictions (several days) and runs daily in operational mode since August 2017. Every day, terabytes of data are produced, manipulated and validated, with highly parallelized software designed at CMCC, to provide the three-dimensional status of the global ocean circulation at a hitherto pioneering resolution of roughly 6 km.
In this work we validate the capability of GOFS16 to provide surface and subsurface realistic initial-state conditions, performing several error analysis against both assimilated and independent datasets. We mainly focus on the validation of currents against satellite-tracked drifter data from the freely accessible Global Drifter Program by NOAA. This will help to discuss its current skill and possible future tuning that can improve, to a large extent, the final quality both at regional and global level.
Global Ocean Dynamics in eddying-regime
Iovino, Doroteaciro;
Masina, Simona;
Pier Giuseppe, Fogli - euro-mediterranean center on climate change (cmcc), Italy
The global ocean is a highly turbulent system over a wide range of space and timescales. Mesoscale eddies pervade the ocean at all latitude bands, and usually account for the peak in the kinetic energy spectrum. Those processes play a substantial role in transporting and mixing temperature and salinity, exchanging energy and momentum with the mean flow, controlling the mechanisms of deep water spreading and deep convection preconditioning, and modulating airsea interactions.
Numerical modelling is an essential tool to represent and understand the climate system, whereof the ocean is a key component. The enhanced realism in representing ocean processes, partially due to increased grid resolution and improved atmospheric forcing, has made the assessment of fidelity of ocean simulations more meaningful and rigorous. It is fundamental to perform simulations in which much of the ocean variability is resolved, and the full dynamics and life cycle of baroclinic eddies are realistically represented.
An advanced numerical approach is presented to characterize mesoscale dynamics in a long-term simulation of the global ocean domain. The GLOB16 configuration, based on state-of-the-art NEMO framework, having 1/16º horizontal resolution at the Equator (increasing up to ~3 km at high latitudes), is used to perform a long hindcast simulation. The experiment design follows a well-established protocol in the ocean modelling community, proposed by the CLIVAR Working Group on Ocean Model Development, that consists in simulating repeating-cycles of the atmospheric forcing dataset. The JRA55-do atmospheric forcing is used over the period 1975 to 2017. This numerical exercise is appropriate for studying the dynamics of the 3D ocean circulation on short timescales, but also to investigate the long-term changes in mesoscale activity. Based on the first-cycle results, analysis of the role of mesoscale features in governing the representation of the ocean mean state and ocean variability is presented.
Use of Remote-Sensed Surface Currents for the Validation of a High-Resolution model of the Mediterranean Sea-Black Sea System
Sannino, Gianmaria;
Bargagli, Andrea;
Carillo, Adriana;
Iacono, Roberto;
Lombardi, Emanuele;
Napolitano, Ernesto;
Palma, Massimiliano;
Pisacane, Giovanna;
Struglia, Maria Vittoria - ENEA, Italy
A high-resolution regional ocean circulation model of the Mediterranean Sea-Black Sea system has been developed and validated against satellite observations of sea height, sea surface temperature, and turbidity.The model is based on the hydrostatic version of the MITgcm (Massachusetts Institute of Technology general circulation model), and includes the effects of the main components of the astronomical tides. The model domain is discretized using 100 vertical z-levels, and a horizontal computational grid of 2500 x 750 points, with a uniform resolution of 1/48° (about 2 km) over most of the domain, increased to a few hundred meters in correspondence of the Straits of Gibraltar, Dardanelles and Bosphorus, in order to correctly resolve the local dynamics. The NEMO operational model provides boundary conditions at the open boundary in the Atlantic Ocean, west of the Gibraltar Strait, while surface forcing is derived from the regional atmospheric high-resolution (5 km) SKIRON model. Climatological discharges for 27 main rivers are included, as derived via the Water Balance Model (WBM; 0.1°x0.1° resolution), driven by WFDEI data.
Model projections appear to be in good agreement with the satellite data used in the first validation exercise, which would greatly benefit from further comparison with additional innovative observational fields. Reliable high-resolution maps of surface currents might prove an invaluable reference for assessing the ability of the model to correctly represent the local patterns of surface circulation.
18:05 - 18:30
08:30 - 09:30
08:30 -
Driving the Ocean Circulation
Stoffelen, Ad;
Belmonte Rivas, Maria - KNMI, Netherlands, The
Surface wind stress and the associated heat and momentum fluxes play an
important role in driving surface and deep ocean circulation. Surface wind
stress modulates the amount of energy available for the ocean gyres (Ekman transport and pumping), initiates ocean stirring by vertical turbulent mixing and triggers deep convection responses.
Many marine forecasting centers (MFCs) use ECMWF-based model input for ocean forcing, with associated NWP model biases.These biases may be quantified using satellite scatterometer winds.
In this contribution we characterize the differences between observed and ERA5/ERA-Interim wind fields in terms of mean and transient winds, wind divergence and stress curl, and the effect of introducing a correction for air-sea relative motion using ocean surface velocities. These mean differences, variables differences and differences due to ocean motion have particulatr impacts on simulating the world ocean circulation. Ways forward to prevent circulation biases will be suggested.
08:45 -
Evaluation of Surface Currents forcing in the CMEMS global Wave System
Aouf, Lotfi (1);
Dalphinet, Alice (1);
Law-Chune, Stephane (2) - 1: Meteo-France, France;
2: Mercator-Ocean, France
A better understanding of physical processes at air sea interface is the important challenge of operational system dedicated to numerical weather and climate predictions. Since April 2018 the global Copernicus Marine Service (CMEMS) wave system is forced by forecasted currents from ocean physical CMEMS system. This study investigates the impact of several currents forcing on the wave forecast at the global scale. We considered different sources of currents from PSY4 ocean system of CMEMS and altimetry currents provided in CMEMS/TAC products. Wave model runs have been performed for long period. The validation of the results has been performed by comparison with altimeters waves data and buoys data. Statistical analysis are discussed for different regional ocean areas which are affected by strong large scale surface currents. We also examined the impact of the time frequency of the currents forcing. Further a focus on tropical ocean is highlighted to analyse uncertainties of surface currents from different sources (altimetry and models).
In order to prepare the CMEMS global wave reanalysis We also performed a sensitivity test of wave model run to surface currents provided by reanalysis GLORYS of global CMEMS.
In other respects wave/currents interactions inducing rogue waves is also investigated by using high order spectral model (HOSM), which provides a more accurate kurtosis in strong currents area such as the Agulhas. For this latter an example will demonstrate how the surface currents enhances the kurtosis and nonlinear instabilities at the sea surface, and consequently increase the probability of occurence of rogue waves.
Further comments and conclusions will be addressed in the final presentation.
09:00 -
Internal Waves, Submesoscale Eddies, and some of their Interactions off the Tropical West Atlantic
da Silva, José Carlos (1);
Magalhaes, Jorge M (1);
Buijsman, Maarten C (2);
Jeans, Gus (3);
Santos-Ferreira, Adriana (1) - 1: University of Porto, Portugal;
2: University of Southern Mississippi;
3: Oceanalysis, Ltd
We reveal that the Amazon shelf break is a powerful hotspot for intense ISWs. These are large amplitude internal solitary waves (ISWs) with vertical displacements of the order of 100 m that become highly nonlinear, with large vertical velocities and heat fluxes that exceed 1000 times the background unperturbed upper-ocean (Shroyer, 2009). Satellite Synthetic Aperture Radar (SAR) data show their two-dimensional horizontal structure and yielded important results concerning their generation and propagation characteristics. Two distinct generation sites were identified off the shelf slopes, each associated with a different pathway of ISWs, but both consistent with an energetics analysis exhibiting high Internal Tide (IT) conversion rates (provided from the Hybrid Coordinate Ocean Model – HYCOM). These largescale waves are characterized by their elevated propagation speeds (up to 3.5m/s) and remote appearance several hundred kilometers away from the nearest forcing bathymetry. These large distances are explained in light of a late disintegration of the IT, based on standard parameters governing the balance between nonlinear and dispersion effects, and the decrease of the waveguide (i.e. thermocline) thickness along a pronounced density front. The waves are refracted in different directions on seasonal and intra-seasonal time scales and their pathways cross mesoscale and submesoscale eddies on occasions. Furthermore, we propose a method to retrieve ISW amplitudes from SAR altimeter measurements (Sentinel-3) and derive current profiles in the water column based on sea level displacements and our knowledge of density climatology. The SAR mode altimeter on board Sentinel-3 is sensitive to surface roughness manifestations originated by dynamic features of various scales in the ocean (Santos-Ferreira et al., 2018). Here we demonstrate a new methodology for automatic detection of high frequency ocean phenomena based on satellite estimation of mean square slopes in the along-track SRAL record. The mean square slope estimates are based on the dual frequency capabilities of Sentinel-3A and 3B radar altimeters, and benefit from the SAR enhanced spatial resolution along-track (300m). Satellite images also reveal that the shelf break is a breeding ground of submesoscale eddies that are formed along the shelf and at the confluence of the NBC and NECC, contributing to shelf-ocean exchange processes. These submesoscale features (eddies and fronts) have significant vertical velocities and associated fluxes, and feed on mixed layer instabilities benefiting from the large Available Potential Energy of the mixed layer depths near the equator. We suggest that the submesoscale vortex street formation results from baroclinic instability due to topographic vorticity generation along the steep slopes of the Amazon shelf.
09:15 -
Satellite Altimeter Combined Measurements :Local Persistent Small-Scale Ocean-Atmosphere Signatures
Chapron, Bertrand (1);
Quilfen, Yves (1);
Collard, Fabrice (2) - 1: Ifremer, France;
2: Oceandatalab, France
Long and energetic surface waves radiating from distant storms may eventually cover a full ocean basin with a lifetime that can extend over a few weeks. Chances are that these swell fields will propagate over regions characterized by strong ambiant upper ocean currents. Resulting interactions can then trigger sea state variability. As particularly analyzed in the Agulhas current region, a dominant regime of incoming southwesterly waves imprints the local wave climatology. Persistent patterns clearly result from the cumulative impacts of the large-scale and persistent nature of the current vorticity field on wave train kinematics. Because of the significant ray deflection and trapping phenomena, localized sea state gradients can be anticipated and are well traced in altimeter signals.
09:30 - 09:35
Developing and Validating High-Resolution Synoptic Measurements of Total Ocean Surface Current and Wind Vectors from Space
Gommenginger, Christine P;
Martin, Adrien C.H. - National Oceanography Centre, United Kingdom
High-resolution satellite images of ocean colour and sea surface temperature reveal an abundance of ocean fronts, vortices and filaments at scales below 10 km but measurements of ocean surface dynamics at these scales are rare. There is increasing recognition of the role played by small scale ocean processes in ocean-atmosphere coupling, upper-ocean mixing and ocean vertical transports, with advanced numerical models and in situ observations highlighting fundamental changes in dynamics when scales reach 1 km. Numerous scientific publications highlight the global impact of small oceanic scales on marine ecosystems, operational forecasts and long-term climate projections through strong ageostrophic circulations, large vertical ocean velocities and mixed layer re-stratification. Small-scale processes particularly dominate in coastal, shelf and polar seas where they mediate important exchanges between land, ocean, atmosphere and the cryosphere. Knowledge of total ocean surface current vectors are relevant also to a multitude of everyday maritime operations including improving fuel-efficiency with ship routing optimization, the siting of marine renewables infrastructure, developing safe and sustainable fisheries and aquaculture and the accurate tracking of oil spills and other pollutants of the marine environment. As numerical models continue to evolve towards finer spatial resolution and increasingly complex coupled atmosphere-wave-ice-ocean systems, modern observing capability lags behind, unable to deliver the high-resolution synoptic measurements of total currents, wind vectors and waves needed to advance understanding, develop better parameterizations and improve model validations, forecasts and projections. SEASTAR is a satellite mission concept that proposes to directly address this critical observational gap with synoptic two-dimensional imaging of total ocean surface current vectors and wind vectors at 1 km resolution and coincident directional wave spectra. Based on major recent advances in squinted along-track Synthetic Aperture Radar interferometry, SEASTAR is an innovative, mature concept with unique demonstrated capabilities, seeking to proceed towards spaceborne implementation within Europe and beyond. This paper will present the current status of the SEASTAR mission and discuss issues surrounding sampling requirements, retrieval accuracy and validation against other current measurements from in situ and remote sensing methods.
EPS-SG SCA Doppler Mode for Ocean Current Estimation
Hoogeboom, Peter (2);
Stoffelen, Ad (1);
Lopez Dekker, Paco (2) - 1: KNMI, DE Bilt, The Netherlands;
2: Tu Delft, Delft, The Netherlands
DOPSCAT has been a study into the capabilities of the SCA instrument on the EUMETSAT EPS second generation (SG) METOP platform for ocean current measurements, but some uncertainties were identified. Since, the Doppler estimation of ocean current with the SCA instrument has been further studied and new, improved simulations have been performed. An innovative method based on pulse-pair transmissions has been developed, which overcomes many of the problems previously encountered. In traditional pulse-pair processing a short time interval between the pulses of the pair, as required by the scene decorrelation time, will lead to range ambiguities if this time interval is shorter than the width of the swath. At first sight, the large scatterometer swath of 660 km (in the order of 4 ms) will surely be a problem. However: the Doppler measurement with the pulse-pair is based on the range responses along the Wind Vector Cell (e.g. 25 km). Due to the relatively high range resolution of 150 m, we obtain a sequence of about 160 (amplitude and) phase responses, which form a unique random phase pattern, which may be tracked in a pulse pair. Note that following general radar backscatter theory, each resolution cell will output a random phase value, but if the time interval between the pulses is short, then the second pulse will generate approximately the same phase as the first one. Only the small movement in range direction of the scatterers will add a phase shift to all the resolution cells. Cross correlation of the WVC responses of the two pulses of a pulse pair will result in a correlation peak at the time difference corresponding to the pulse pair time interval. The phase at the correlation peak is proportional to the displacement of the scatterers in the WVC, hence the ocean current. The correlation method resembles the processing of a noise radar. A brief analysis based on Cramer-Rao maximum obtainable range accuracy demonstrated a limit value of approximately 0.8 m/s for a 25 x 25 km WVC.
SCA is designed to measure high-accuracy ocean vector winds and complementary collocated Doppler shift measurements would be highly valuable to analyze the ocean surface motion and incur some ocean current information from it. It cannot be expected that the quality of such combined measurements can fulfil the most stringent requirements of the oceanographic community, but on the other hand, if it is possible with a small effort to enhance the products of SCA with an ocean current product, than that is certainly valuable, even if other dedicated ocean current missions are under investigation. The current study shows promising results for a new and innovative way of measuring the ocean current vector. The precision is below 0.5 m/s for a 50x50 km WVC. A more detailed study is recommended, along with real system data testing. Many factors that influence the performance still require attention, e.g., the improvement of statistical reliability, platform attitude accuracy, investigation of other waveforms, realistic SNR inclusion in the simulation, better ocean surface models.
09:30 - 10:00
10:00 - 10:30
10:30 - 12:30
10:30 -
DUACS Altimetry-Derived Current Products Status And Perspectives
Faugere, Yannice (1);
Pujol, Isabelle (1);
Ubelmann, Clement (1);
Maxime, Ballarotta (1);
Taburet, Guillaume (1);
Dibarboure, Gerald (2);
Picot, Nicolas (2) - 1: CLS, France;
2: CNES, France
The DUACS system produces, as part of the Copernicus Marine Environment and Monitoring Service, high quality multi-mission altimetry Sea Level products, along-track cross-calibrated SLA (Level3) and multiple sensors merged as maps (Level 4) for oceanographic applications, ocean circulation studies, climate forecasting centers, geophysic and biology communities... One of the variables of the Sea Level product is the geostrophic current (anomalies and absolute) directly deduced from the topography. The CMEMS/Sea Level team maintains the 25 year time-series corresponding to the altimetry era (1993-2018) and produce in real time (3 hours) global and regional products (Mediterranean Sea, Arctic, European Shelves …), available through the CMEMS web portal.
In 2018 the whole time series has been entirely reprocessed with the latest altimetry standards and refined L3/L4 processing. The new products, widely assessed in terms of Sea Level and ocean current, exhibits better performances regionally and in the coastal areas. Comparison with drifters notably showed strong improvement in the tropics (Taburet 2019). The use of magnitude square coherence between the grid and independent along track data also helped to characterize the grids effective resolution, ranging from 600km at the equator to 100km at high latitude (Ballarotta, 2019).
In the coming two years, strong perspectives are expected. To the 6 altimetry missions currently ingested in the system (Jason-3, Sentinel3A, Altika, Cryosat-2, Jason-2 and HY2A) several will be added as Sentinel3B, CFOSat, HY2B. This configuration with 2 SAR mode mission, and at least 5 LRM mission is unprecedented. Moreover, recent development enabled to optimize the SAR processing (Boy 2017, Moreau,2018) and the LRM noise level (Zaron 2016, Tran 2019) and will allow us to fully exploit the fine-scale content of the altimetric missions and propose ocean Level3 products at 1km resolution. The mapping of geostrophic current can be improved regionally thanks to refined merging method (Ubelmann, 2016) or the use of drifters speed to complement the altimetry information notably in the meridional direction through a multivariate analysis. Finally, the use of High Resolution MDT solution (1/8eme) will give access to improved absolute current.
This presentation will give an overview of the DUACS altimetry-derived current products, the operational products delivered as part of CMEMS, as well as demonstration products (https://www.aviso.altimetry.fr/duacs), and will discuss the perspectives for the two coming years.
10:45 -
Recent Progresses in Coastal and Open Ocean Altimetry and their Possible Applications for Circulation Studies
Passaro, Marcello (1);
Boergens, Eva (1);
Chereskin, Teresa K (2);
Dettmering, Denise (1);
Gille, Sarah (2);
Gomez-Enri, Jesus (3);
Müller, Felix L (1);
Piccioni, Gaia (1);
Quartly, Graham D (4);
Schwatke, Christian (1);
Smith, Walter HF (5) - 1: Technische Universität München, Germany;
2: Scripps Institution for Oceanography, USA;
3: University of Cadiz, Spain;
4: Plymouth Marine Laboratory, UK;
5: National Oceanic and Atmospheric Administration, USA
Satellite Altimetry is a powerful tool to estimate ocean currents. 25 years of altimetry data have revealed the details of the large scale geostrophic circulation. Multi-mission dataset are now used to describe the dynamic topography with unprecedented detail. Data from Satellite Altimetry are also used to feed circulation models.
Despite these progresses, several challenges remain ahead. In particular, the noise level of altimetry data is still too high to get an insight into the middle-to-low scales of variability. This is even more true in the coastal zone, where the accuracy of satellite altimetry data is undermined by a number of factors: difficulties in fitting the radar altimetry echoes, lower accuracy of the corrections needed to extract the sea level anomaly starting from the range (distance between satellite and sea surface) estimation, high variability and small scale features typical of shelf seas and oceanic slopes.
This talk will be a review of recent progresses and work in progress that are promising for exploitation in terms of circulation studies. Indeed, improving the precision of satellite altimetry and extending the records to the coastal zone could have positive impacts for circulation studies, which shall be investigated. Delivering more precise sea level data means decreasing the need for strong filtering when deriving geostrophic velocities. Exploiting coastal altimetry means observing coastal circulation in areas where in-situ data are scarce.
Topics that will be considered are:
1) Advances in the availability of coastal altimetry data in connection to improved fitting of the altimetry waveforms (retracking), corrections and the use of Delay-Doppler altimetry on Sentinel-3 and Cryosat-2.
2) Analysis of the localised impact of dedicated coastal altimetry dataset on describing the circulation, with a case study in the Strait of Gibraltar
3) New understanding in interpreting part of the “Sea State Bias” correction as retracking-related noise, which would deliver high-frequency altimetry data with about 30% of improvement in precision
4) On-going efforts in improving the significant wave height determination from Satellite Altimetry, which could be useful to increase our understanding of the waves-currents interaction
The talk will also call for answers that are needed for open questions such as: what kind of circulation features are captured by satellite altimetry for scales lower than ~50 km and how can satellite altimetry work in synergy with other techniques to achieve this goal?
11:00 -
High Resolution Surface Current From The Synergetic Use Of Altimetry, Sea Surface Temperature, Wind And In Situ Measurements
Etienne, Hélène (1);
Rio, Marie-Hélène (2);
Mulet, Sandrine (1);
Greiner, Eric (1);
Dibarboure, Gérald (3);
Picot, Nicolas (3);
Donlon, Craig (4);
Guinehut, Stéphanie (1) - 1: CLS, France;
2: ESA-ESRIN, Italy;
3: CNES, France;
4: ESA-ESTEC, The Netherlands
Accurate estimate of ocean surface currents is both a challenging issue and a growing end-users requirement. The most exploited system for the monitoring of ocean surface currents at global scale is so far spaceborne altimetry observations, the flow in the ocean interior and away from the equator being at first order in geostrophic balance. Three complementary observations-based approaches have been developed to correct the altimeter-derived geostrophic currents and to obtain more realistic upper ocean surface circulation fields in terms of physical content and spatial and temporal resolution. These developments have been carried out through CNES/CLS projects as well as during the Globcurrent project (funded by the ESA User Element Program). Operational products are now available through CMEMS MULTIOBS component and experimental products are available through AVISO and Globcurrent portals.
The first approach combines the geostrophic and Ekman components of the circulation. The geostrophic component is derived from altimeter multimission fields (SSALTO-DUACS component, distribution by CMEMS Sea Level Thematic Assembly Center) and the CNES-CLS13 Mean Dynamic Topography. The Ekman component is available at two depths (surface and 15m) and is computed using an empirical model forced by wind-stress fields. The empirical model parameters (amplitude and angle) are derived using wind-stress fields and collocated in-situ velocities (Argo floats at the surface and SVP drifters at 15m depth) from which the geostrophic component and high frequency motion has been extracted. The surface and 15m Ekman currents show a spiral-like response to wind stress in good qualitative agreement with the theory.
The second approach uses the synergy between spaceborne altimetry and Sea Surface Temperature observations. The method is based on the inversion for the velocity of the heat conservation equation using the altimeter-derived geostrophic currents as background. By accurately prescribing the error both on the background velocities and on the forcing term (heat fluxes), the surface velocities are successfully improved in areas characterized by strong SST gradients and remain unchanged in low SST gradient regions, where by construction no additional information is brought by the SST field. Both the spatial and temporal resolutions of the altimeter derived velocities are enhanced by the SST information.
The third approach uses the synergy between spaceborne altimetry and in situ velocities observations which provide essential and complementary information on the position and displacement of mesoscale structures. The method is based on a multivariate optimal interpolation mapping method using both observations of height and velocities and prior statistical knowledge of the field to be estimated. It allows both to improve the ocean surface currents and height where the density of the in situ observations is sufficient.
First two approaches have been applied globally and long time series are available (1993-onwards). The third approach has been tested at regional scale in the Gulf of Mexico and for a one-year period. All have been validated using independent in situ observations and intercompared. Development prospects include improvement paths for each method and the combination of the three approaches.
11:15 -
Indirect Determination of Ocean Surface Currents: Available Approaches and Gaps
Isern-Fontanet, Jordi - Institut de Ciencies del Mar (CSIC), Spain
Ocean currents play a key role in Earth’s climate – they impact almost any process taking place in the ocean and are of major importance for navigation and human activities at sea. Nevertheless, their observation are still difficult because direct measurements of global ocean currents on synoptic scales are scarce. Consequently, it has been necessary to use sea surface height and sea surface temperature measurements and refer to dynamical frameworks to derive the velocity field. In this talk we review the current knowledge in these fields, we provide a global and systematic view of the approaches to retrieve ocean velocities in the upper ocean and we discuss the actions necessary to implement these approaches for the operational generation of satellite-based ocean velocities.
11:30 -
An Assessment of MCC Techniques with Modern Sensors
Quartly, Graham Duncan;
Warren, Mark - Plymouth Marine Laboratory, United Kingdom
The Maximum Cross Correlation (MCC) technique infers motion by comparing images a short interval apart and noting how features have moved between them. It was first applied to Earth Observation data more than three decades ago, and has gone through various periods of popularity since. Early work used brightness temperature images from AVHRR at 1km resolution, with images either 6, 18 or 24 hours apart. The recent resurgence of interest has been fuelled by the high-resolution images available from geosynchronous satellites at intervals of a few hours. Example datasets are the ocean colour data from GOCI and the infra-red data from SEVIRI. A compromise needs to be struck between using images well separated in time to give good velocity resolution, and wanting to apply the analysis over short intervals to resolve temporal variations such as tides. A further problem with long intervals is that the motion may no longer be adequately described by translation, as the features rotate or evolve by being sheared. Another compromise is in the choice of size of template and the search radius used in the second image: small values enable quick processing, whereas larger templates and search areas are slower but can be more robust in their correct matching of features.
Some challenges still remain. One is dealing with the coast, as a simplistic implementation of MCC will not cope easily with large patches of "missing data" in the marine image that do not move along with the oceanographic features. The second challenge, for optical systems, is the patchiness of data due to cloud cover. Whilst a series of images with gaps due to clouds may be readily composited to give a mean view, a technique that relies on features being recognisably present in two or more images is much more sensitive to intermittent data loss. In polar environments some success has been had with SAR sensors, which may have a short revisit time at high latitudes, and can be used to infer currents through their advective effect on pieces of sea-ice. Such analysis may become particularly viable in the near future with the launch of the RadarSat Constellation in 2019 providing more frequent coverage of these latitudes.
11:45 -
Spatio-Temporal Relationships between SSH and SST and/or SSS Fields
Reul, Nicolas;
Chapron, Bertrand;
Autret, Emmanuelle - Ifremer, France
Multisatellite measurements of altimeter-derived sea surface height (SSH), sea surface temperature (SST), and sea surface salinity (SSS) provide a wealth of information about ocean circulation, particularly mesoscale ocean dynamics which may involve strong spatio-temporal relationships between SSH and SST and/or SSS fields. Within an observation-driven framework, we investigate the extent to which mesoscale ocean dynamics may be decomposed into a mixture of dynamical modes, characterized by different local regressions between SSH, SST and SSS fields.
12:00 -
Zonal Equatorial Current Mapping With Sentinel-1 Wave Mode Calibrated Doppler
Collard, Fabrice (1);
Guitton, Gilles (1);
Johnsen, Harald (2);
Engen, Geir (2);
Recchia, Andrea (3);
Bras, Sergio (4) - 1: OceanDataLab, France;
2: NORUT, Norway;
3: ARESYS, Italy;
4: ESA ESTEC, Netherland
Recent activities to define a calibration strategy for Sentinel-1 Level 2 RVL component of OCN product is demonstrated on two month of Sentinel-1B Wave Mode dataset. This new strategy is based on a combinaison of data driven calibration for the slow time variations at the scale of the orbital period or more, and accurate on-ground calibration and processing of Gyroscope telemetry for the fast variations. The overall calibration allow to improve the geophysical Doppler shift accuracy to better than 5 Hz, allowing accurate estimation of the radial component of total ocean surface current, after correction of the wave induced Doppler bias, also estimated from the data itself, exploiting the high wavenumber part of the cross-spectra. Results are compared to in-situ measurements of 15m depth surface current from drifter climatology.
12:15 -
Uncovering Finescale Ocean Vertical Currents from the Synergy of In Situ and Satellite Observations
Pascual, Ananda (1);
Ruiz, Simon (1);
Barceló-Llull, Bàrbara (2);
Sánchez-Román, Antonio (1);
Mason, Evan (2);
Cutolo, Eugenio (1);
Rodríguez-Tarry, Daniel (1) - 1: IMEDEA(CSIC-UIB), Spain;
2: Universtity of Washington, US
Vertical motions associated with mesoscale (10-100 km) and submesoscale (1-10 km) ocean features, such as fronts, meanders, eddies and filaments, play a critical role in the exchange of heat, fresh water and biogeochemical tracers between the surface and the ocean interior. Integrating our understanding of these processes to climate scales is one of the key challenges for earth observation, limited by the high resolution of the oceanic data that is required to estimate dynamic vertical transports.
In this talk we review some of the results obtained over the last 15 years from attempts to estimate vertical motion through application of the QG-omega equation from a combination of in-situ (CTD, glider, Argo, XBT, ADCP, …) and satellite observations (altimetry, SST ,…) during dedicated multi-platform field experiments as well as from synthetic fields.
We conclude with the lessons learnt in terms of advantages and limitations of the present approaches that combine satellite data with other cutting-edge and well established observational techniques and numerical modeling. Future directions of research are also addressed, including the need to observe and resolve a range of scales that will contribute to enhancing our understanding of intense but transient vertical exchange in the ocean that is associated with meso- and submesoscale features, with impacts on longer climatic scales.
12:30 - 13:30
13:30 - 15:00
13:30 -
3D Upper Ocean Circulation From The Combined Use Of In Situ And Spaceborne Observations
Guinehut, Stephanie;
Mulet, Sandrine;
Verbrugge, Nathalie;
Etienne, Helene;
Greiner, Eric - CLS, France
Producing comprehensive information about the ocean has become a top priority to monitor and predict the ocean and climate change. Complementary to modeling/assimilation approaches, an observation-based approach is proposed as part of CMEMS MULTIOBS component. It relies on the combination of spaceborne (altimetry (SLA), sea surface temperature (SST) and sea surface salinity (SSS)) and in situ (temperature and salinity profiles) observations through statistical methods (Guinehut et al., 2012; Mulet et al., 2012).
The methods have been developed to take advantage of the strength of the two main components of the Global Ocean Observing System, namely, the sparse but accurate and 2D (vertical) in situ observations and the high resolution in space and time but integrated or surface satellite observations. The method uses first a multiple linear regression method to derive synthetic T/S profiles from the satellite measurements (SLA, SST, SSS). These synthetic profiles are then combined with all available in-situ T/S profiles using an optimal interpolation method. The thermal wind equation with a reference level at the surface is finally used to combine surface geostrophic current fields from satellite altimetry with the thermohaline fields to generate the global 3D geostrophic current fields.
Global temperature, salinity and geostrophic current fields are produced at a weekly period, on a 1/4° horizontal resolution grid from the surface down to 1500-meter depth. A reprocessing is available from 1993 onwards. The capacity of MULTIOBS products and system will be illustrated through various applications: 1) systems intercomparison (essentially between various CMEMS products – global or regional), 2) observing system evaluation, 3) ocean state estimate, 4) mesoscale eddies studies.
Development prospects include the combination with surface currents fields, such as the ones also available through CMEMS MULTIOBS component known as COPERNICUS-GLOBCURRENT (see abstract from HEtienne et al., High resolution surface currents from the synergetic use of altimetry, sea surface temperature, wind and in situ measurements) using an analytical formulation at depth for the Ekman component of the circulation.
13:45 -
Estimating 3D Ageostrophic Motion in the Oceans: operational perspectives and future challenges
Buongiorno Nardelli, Bruno (1);
Mulet, Sandrine (2);
Guinehut, Stephanie (2);
Iudicone, Daniele (3) - 1: Consiglio Nazionale delle Ricerche, Italy;
2: Collecte Localisation Satellites, France;
3: Stazione Zoologica Anton Dohrn, Italy
First order dynamical balances in the oceans describe a predominantly horizontal and quasi-stationary circulation. However, small departures from geostrophy can drive intense vertical exchanges at depth, modulating the ocean thermohaline circulation, as well as affecting the marine ecosystem dynamics. The estimation of 3D vertical velocities from observations thus remains one of the main challenges for years to come. In the framework of the Copernicus Marine Environment Monitoring Service (CMEMS), an observation-based global dataset of vertical velocities has been developed and will be soon distributed through the CMEMS Multi-Observation Thematic Assembly Centre. Vertical velocities are inferred by applying a diabatic version of the quasi-geostrophic Omega equation to a 3D reconstruction of density and geostrophic velocities, based on the statistical combination of surface information from satellite data and in situ profiles. Strengths and limitations of the present retrieval, as well as future operational perspectives, will be discussed and reviewed.
14:00 -
Perspectives for Surface Current reconstruction combining SKIM and altimetry
Ubelmann, Clement (1);
Dibarboure, Gerald (2) - 1: CLS, France;
2: CNES, France
In the context of an altimetry constellation observing the large scales (above 200km wavelength) of geostrophic currents, it is worth exploring the potential synergy with observations of the full surface current such as SKIM. This later includes geostrophic motions, but also Ekman, inertial oscillations, tidal (barotropic and baroclinic) surface currents and other ageostrophic processes.
Observing the sum of these components has an obvious added value to the single geostrophic component presently observed. In this study, we propose to quantify the contribution of the two observing systems combined to map the mesoscale (100km,10days) circulation.
Observing System Simulation Experiments (OSSEs) are conducted from very high resolution simulations resolving all components of the surface currents and topography. A multivariate optimal interpolation scheme is used to combine along-track topography with radial velocity synthetic observations unevenly distributed in time and space, following the sampling of the SKIM design (Ardhuin et al., 2017). Prescribing accurate covariances for both topography and currents, accounting for all components and their best linear dependences (cross current/topography terms) is the challenge for exploiting the synergy. In a few key regional configurations (western boundary current, low-latitudes, eastern basins, …) we will quantify the mesoscale reconstruction with each system separately and with their combination, through metrics of residual errors and effective resolution of the signal.
14:15 -
Exploiting from Multi-Sensor Synergy to Track Dynamical Structures
Gaultier, Lucile;
Collard, Fabrice;
Guitton, Gilles;
Herlédan, Sylvain;
El Khoury Hanna, Ziad;
Le Séach, Guillaume - OceanDataLab, France
New satellites and sensors arose during the past decade, enabling to observe a wide range of oceanic physical variables at various scales. For example, the Sentinel 1-2-3 program covers various sensor such as SAR, Ocean Color, Temperature brightness or altimeter with an individual revisit not better than daily but with a quite rapid revisit from a constellation point of view. All these variables contains important information regarding the upper ocean dynamics even indirectly. Thus there is a need to find new avenues to exploit the wealth of available remote sensing data by considering them as structured information rather than pointwise data. Moreover, handling this huge heterogeneous dataset has never been easier using the Ocean Virtual Laboratory online portal (https://ovl.oceandatalab.com) or the standalone version (https://seascope.oceandatalab.com), enabling to visualise heterogeneous satellite and in-situ observations collocated in time and space.
First, we will present a method to extract dynamical information contained in tracer like observation such as the Sea Surface Temperature to improve the assessment of surface oceanic current derived from altimetry. Then, we will demonstrate few examples of data synergy using the Sentinel 1-2-3 on the Ocean Virtual Laboratory and show how to inter-compare detected structures and validate the detection of oceanic fronts and eddies. Finally, we will consider all the Sentinel observations to build synoptic chart and show how ship routing can benefit from these methods.
14:30 -
Improving the monitoring of Coastal Circulation from the combined use of Altimetry and a Coastal HF Radar
Caballero, Ainhoa (1);
Rubio, Anna (1);
Ayoub, Nadia (2);
Dufau, Claire (3);
Davila, Xabier (2);
Mader, Julien (1);
Manso-Narvarte, Ivan (1);
Mulet, Sandrine (3);
Larnicol, Guilles (3) - 1: AZTI, Spain;
2: LEGOS, France;
3: CLS, France
Each remote sensing technique for inferring ocean circulation is designed for measuring certain scales and has its own pros and cons. A necessary step forward in the combination of data from different remote sensing sources into new integrated observational products, is the study of their complementarity. In the framework of the COMBAT Project (CMEMS Service Evolution 2), the potential combination of altimetry and coastal HF radar data is assessed. The final goal of this exercise is to use the existing long time-series of high-quality HF radar velocity measurements in the southeastern Bay of Biscay, for computing an improved local solution of the Mean Dynamic Topography. A prerequisite for the computation of this new Mean Dynamic Topography is to remove the non-geostrophic signal from the measured velocities and to know better the scales resolved by the altimetry in the study area. Forth is purpose, outputs from two different regional numerical models have been used. Model simulations are used herein for a better understanding of the processes contained in both databases. Then, different methods for isolating the geostrophic currents from the HF radar total currents are tested. First results show a reasonable agreement between HF radar currents and outputs from regional numerical models. The agreement depends on the regional model used and their configuration. The coastal observatory of the southeastern Bay of Biscay will benefit from an improved estimation of its complex coastal circulation and for defining future developments in this operational observing system. Different downstream applications will finally illustrate the impact of this improved integration of observations into key coastal issues (environmental services for marine litter management and maritime safety).
14:45 -
Quantifying The Impact Of Dynamical Constraints For Reconstructing Surface Currents
Barth, Alexander (1);
Charles, Troupin (1);
Reyes, Emma (2);
Tintoré, Joaquín (2);
Beckers, Jean-Marie (1) - 1: University of Liege, Belgium;
2: SOCIB, Spain
High-Frequency (HF) radars is a land-based remote sensing technique allowing to measure coastal ocean surface currents. They explore the scattering of surface-coupled electromagnetic waves to determine the doppler-shift induced by ocean currents to determine the radial surface velocity relative to the HF radar site. By combining two or more HF radar sites one can derive total vector currents (composed by zonal and meridional velocity) from the radial currents. As any indirect remote sensed measurements, HF radar ocean surface currents can be affected by several sources of noise and uncertainties. Also several gaps can be present in the direct radial currents fields.
Combining the radial currents with the knowledge of the underlying dynamics can provide a current analysis over the entire domain and potentially also reduce the noise in the observations. In the present work we quantify the benefit of including dynamical constraints to optimize an ocean surface current analysis using the data analysis tool DIVA (Data-Interpolating Variational Analysis).
DIVA is commonly applied to in situ observations such as temperature, salinity or nutrient concentration to obtain gridded climatologies. It takes the coastline and bathymetry, ocean currents and the spatial connectivity of water bodies into account to interpolate these tracers, also considering uncertainties on observations. For vector quantities, like ocean surface currents, a new set of constraints relevant to surface currents have been taken into consideration, including imposing a zero normal velocity at the coastline, imposing a low horizontal divergence of the surface currents, temporal coherence and simplified dynamics based on the Coriolis force and possibly including a surface pressure gradient.
The impact of these constraints is evaluated by cross-validation using the HF radar surface current observations in the Ibiza Channel from the Balearic Islands Coastal Ocean Observing and Forecasting System (SOCIB). A small fraction of the radial current observations are set aside to validate the velocity reconstruction. The remaining radial currents from the two radar sites are combined to derive total surface currents using DIVA and then compared to the cross-validation data set. The benefit of the dynamic constraints is assessed relative to a naive variational interpolation ignoring these dynamical constraints. Best results have been obtained when the Coriolis force and the surface pressure gradient are included together. A similar validation exercise was also performed using drifter trajectories deployed by SOCIB leading to the same conclusion.
15:00 - 15:30
Validation of Ocean Surface Current Retrievals from Sentinel-1 IW Doppler Shift Using HF-radar and Lagrangian Drifters Observations of the Norwegian Coastal Current
Moiseev, Artem (1);
Johnsen, Harald (2);
Hansen, Morten (1);
Johannessen, Johnny (1) - 1: The Nansen Center, Bergen, Norway;
2: Northern Research Institute, Tromsø, Norway
The ocean circulation is responsible for a significant transport of heat and salt, and play a major role for climate and weather. Knowledge of surface currents is crucial for oil spill and marine debris tracking, search and rescue operations, and fisheries as well as essential for the provision of reliable sea state forecasts for maritime operations and ship routing. Therefore, accurate estimation and systematic monitoring of the surface currents is essential for marine research and operations, especially in the coastal zones where most of the human activities are located.
Conventional observation methods include in-situ point measurements from buoys or moorings, and Lagrangian drifters. Moreover, land-based remote sensing systems, such as High-Frequency radars (HFR) have also been proved to be an indispensable source for spatial mapping of ocean currents in the near-coastal zone. Unfortunately, pour spatial coverage and high deployment cost for the in-situ sensors, as well as limited spatial coverage of HFR (maximum up to 220 km from the sensor), along with other limitations, disable systematic spatial monitoring of the surface currents.
Sentinel-1 IW Level 2 OCN products available on a regular basis (up to two times per day) in the coastal zone. Hence, the corresponding retrieval of the surface currents from SAR acquisitions can be used for filling observation gaps in areas not covered by in-situ and land-based remote sensing measurements. However, a careful validation of the SAR derived surface current estimates through systematic collocation with other remote sensing and in-situ datasets is therefore required.
In this study results of the evaluation of these range surface current velocities derived from Sentinel-1A IW VV Level 2 Doppler frequency shifts acquired over the northern coast of Norway are presented and compared to CODAR SeaSonde (HFR) and lLagrangianocean surface drifters (CATHE) observations. In addition, the data are collocated with the 8-day average Sea Surface Temperature (SST) fields from MODIS-Aqua L3 products.
Significant signatures of the Norwegian Coastal Current can be observed in most of investigated SAR acquisitions. These features are also visible in the 8-days average SST maps. Comparison of the SAR derived radial velocities to the CODAR SeaSonde observations shows significant correlation with mean bias about 0.04 m/s and RMSE 0.37 m/s. In addition, also the collocation of the SAR radial velocities with the ocean surface velocities obtained from drifters shows good correlation. However, accurate retrieval of the surface current velocity from a single SAR image still has limitations due to the residual bias in Doppler centroid calibration and uncertainty due to the wind/wave bias contribution to the acquired signal. The latter is most likely arising from inaccurate model estimates of the wind speed and direction. The preliminary results suggest that the best agreement are derived for moderate winds in the range direction.
A Parametric Representation to Integrate Current Observations into the Estimation of the Mean Dynamic Topography
Brockmann, Jan Martin;
Neyers, Christian;
Fenoglio-Marc, Luciana;
Schuh, Wolf-Dieter - Institute of Geodesy and Geoinformation, University of Bonn, Germany
The geodetic estimation of the mean dynamic ocean topography (MDT) as the difference between the sea surface height (SSH) and the geoid remains, despite the simple relation, still a difficult task. Mainly, the spectral inconsistency between the available altimetric SSH observations and the geoid causes problems in the separation process. This is complemented by the accuracy characteristics of the satellite derived geoid information, as it is only sufficiently accurate for a resolution of about 100 km (even when using state-of-the art global GOCE based geoid models). As soon as further observations are integrated, which can be linked only to the MDT, the separation process is strongly supported. One type of information which can be used are (geostrophic) currents.
Within a national DFG project, we study parametric approaches which represent the MDT by a mathematical function. In contrast to the commonly used grid based approaches – which provide function values on a predefined grid – the mathematical surface is continuously defined. Within the project we are working on the use of finite element spaces, which are tailored to represent the MDT. With a focus on C1 -smooth finite elements, the surface as well as its first derivatives, which are related to the geostrophic currents, are smooth. Via the derivative of the surface, which can be analytically computed, the geostrophic currents can be directly evaluated in the region of interest.
The MDT, represented by the scaling coefficients of the finite element base functions, is estimated together with the geoid from altimetric along-track sea surface height measurements and stochastic geoid information (satellite based gravity field normal equations). With this independent geoid information, the altimetric SSH can be separated into the geoid and the MDT within the common resolution. The finite elements serve as a spatial filter, an additional filtering is not required. The temporal averaging is directly done by the adjustment. In case realistic error models for the altimetric SSH as well as for the geoid is used, accuracy information for the derived MDT can be provided. This can be propagated to the derived geostrophic currents, such that they can be tested for statistical significance.
Due to the parametric nature of the proposed representation, it is possible to integrate any observation which can be linked to either the geoid, or the MDT into the estimation process. Possible observation groups are geostrophic current observations derived from surface drifters or, as in focus of the current project, SAR derived radial surface velocities (if they can be reduced to the geostrophic constitute). Although they only contain a radial part of the currents, their integration into the estimation of the MDT will support the separation of the SSH measurements. Although the quality of the actual available products, e.g. from Sentinel-1, is not sufficient, we are working on the methodology to integrate those type of observations. Within the contribution, we will summarize the basic ideas of the approach and present the status of our work.
The New CNES-CLS18 Mean Dynamic Topography
Mulet, Sandrine (2);
Rio, Marie-Hélène (1);
Etienne, Helene (2);
Picot, Nicolas (3);
Dibarboure, Gerald (3) - 1: ESA/ESRIN, Italy;
2: CLS, France;
3: CNES, France
The Mean Dynamic Topography (MDT) is a key reference surface for altimetry. It is needed for the calculation of the ocean absolute dynamic topography, and under the geostrophic approximation, the estimation of surface currents. Those are required for a wide range of applications as the management of fishery resources, the monitoring of potential pollution, maritime security… Also, the MDT is the missing component for the optimal assimilation of altimeter data into operational ocean system as those run under the Copernicus Marine Environment Monitoring Services (CMEMS).
CNES-CLS Mean Dynamic Topography solutions are calculated by merging information from altimeter data, GRACE and GOCE gravity data and oceanographic in-situ measurements (drifting buoy velocities, hydrological profiles). Objective of this communication is to present the newly updated CNES-CLS18 MDT. The main improvements compared to the previous CNES-CLS13 solution is the use of updated input datasets: the GOCO05S geoid model (instead of DIR4) is used together with all drifting buoy velocities (SVP-type and Argo floats) and hydrological profiles (CORA database) available from 1993 to 2017 (instead of 1993-2012). The new solution also benefits from improved data processing (in particular a new Ekman model is used to extract the geostrophic component from the buoy velocities) and methodology (in particular the correlation scales used for the multivariate mapping have been revised). An evaluation of the new solution compared to the previous version and to other existing MDT is done through comparison to independent in-situ data.
Ubiquitous Sensing And Omni-Situ Surface Currents
Guichoux, Yann;
Le Goff, Clement - eodyn, France
Our presentation focus on the description of a new technique allowing omni-situ ocean surface currents measurements relying on environmental data sets and ship motions data analytics. The technology makes it possible to retrieve real time and historical ocean surface currents information at a global scale. First the technique is introduced, how machine learning on environmental data sets and ship motions can produce omni-situ ocean surface currents. Performances are assessed showing results in different ocean dynamic conditions, comparing HF radar measurement, drifters and geostrophic currents derived from altimetry with eOdyn products. Technology fields of application, as well as its limitations and development status are introduced. Finally, results showing how Omni-Situ currents can complement altimetry and Doppler measurements from space are presented.
Ocean Transport and Dynamical Systems: Applications and Perspectives
Mancho, Ana Maria - CSIC, Spain
Finding order in the apparent chaos that seems to govern transport processes in the ocean is a challenge. Dynamical system tools, such as Lagrangian Descriptors [1,2,3], reveal beautiful time dependent geometries in the ocean that comprise an efficient underlying transport network. Silbo, one of the first transoceanic autonomous underwater vehicle missions has corroborated the presence in the ocean of these dynamical structures and their capability to achieve unprecedented speed ups of the glider [4]. Additionally the evolution of the fuel spill subsequent to the sinking of the Oleg Naydenov fishing ship in the Gran Canaria coast, Spain in April 2015, confirmed that this dynamical template accurately described the long-time behavior of fuel blobs, identifying potentially dangerous regions for these types of oil spill disasters and the arrival points of slicks to the coast [5]. Finally, relevant findings in upper Arctic waters are also discussed [6].
References
[1] C. Mendoza, A. M. Mancho. Phys. Rev. Lett. 105, 3, 038501, (2010).
[2] A. M. Mancho, S. Wiggins, J. Curbelo, C. Mendoza. Commun. Nonlinear Sci. Numer. Simul. 18, 3530-3557 (2013).
[3] C. Lopesino, F. Balibrea-Iniesta, V. J. García-Garrido, S. Wiggins, A. M. Mancho. Int. J. Bifurcation Chaos 27, 1730001 (2017).
[4] A. G. Ramos, V. J. García-Garrido, A. M. Mancho, S. Wiggins, J. Coca, S. Glenn, O. Schofield, J. Kohut, D. Aragon, J. Kerfoot, T. Haskins, T. Miles, C. Haldeman, N. Strandskov, B. Allsup, C. Jones, J. Shapiro. Sci. Rep. 8, 4575 (2018).
[5] V. J. Garcia-Garrido, A. Ramos, A. M. Mancho, J. Coca, S. Wiggins. Mar. Pollut. Bull. 112, 201-210, (2016).
[6] F. Balibrea-Iniesta, J. Xie, V. J. García-Garrido, L. Bertino, A. M. Mancho, S. Wiggins. Quaterly Journal of the Royal Meteorological Society (in press) (2018).
Support from ONR grant No. N00014-17-1-3003 is acknowledged.
Retrieval Of Ocean Currents From SMOS
Olmedo, Estrella (1,2);
González-Haro, Cristina (1,2);
Isern-Fontanet, Jordi (1,2);
González-Gambau, Verónica (1,2);
Turiel, Antonio (1,2);
Martínez, Justino (1,2) - 1: Institut de Ciències del Mar (CSIC), Spain;
2: Barcelona Expert Center BEC, Spain
Horizontal surface density gradients in the ocean are responsible for surface geostrophic currents on scales where Earth rotation is important. These currents are systematically computed using along-track altimetric measurements of sea surface height (SSH), but the limited number of altimeters can lead to errors in their location [Pascual et al., 2006]. On the other side, satellite measurements of sea surface temperature (SST) are better suited to locate flow patterns under the appropriate environmental conditions and can be exploited to retrieve density anomalies and, thus, velocities at the ocean surface through the Surface Quasi-Geostrophic (SQG) approach [Isern-Fontanet et al., 2006a]. However, in some areas salinity contribution to density may dominate over temperature contribution, which can induce wrong signs in the vorticity retrieved from SST. This situation can be found in the Algerian Basin [Isern-Fontanet et al., 2014], which is located at the entrance of the Mediterranean Sea. A recent work demonstrated that SMOS SSS maps capture the key dynamics of Algerian eddies allowing to retrieve velocities from SSS with the correct sign of vorticity [Isern-Fontanet et al., 2016].
In this work, we plan to assess the capability of the new L2 SSS product developed at the Barcelona Expert Center for reconstructing ocean surface currents at a global scale following an SQG-like regim. This L2 product is retrieved using a debiased non-bayesian approach similar to the one described in [Olmedo et al. 2017].
References
Isern-Fontanet, J., B. Chapron, P. Klein, and G. Lapeyre (2006a), Potential use of microwave SST for the estimation of surface ocean currents, Geophys. Res. Lett., 33, L24608, doi:10.1029/2006GL027801.
Isern‐Fontanet, J., E. Olmedo, A. Turiel, J. Ballabrera‐Poy, and E. García‐Ladona (2016), Retrieval of eddy dynamics from SMOS sea surface salinity measurements in the Algerian Basin (Mediterranean Sea), Geophys. Res. Lett., 43, 6427–6434. doi:10.1002/2016GL069595
Pascual, A., Y. Fauge`re, G. Larnicol, and P. Le Traon (2006), Improved description of the ocean mesoscale variability by combining four satellite altimeters, Geophys. Res. Lett., 33, L02611, doi:10.1029/2005GL024633.
Olmedo, E., Martínez, J-, Turiel, A., Ballabrera-Poy, j., Portabella, M. Debiased non-Bayesian retrieval: A novel approach to SMOS Sea Surface Salinity, Remote Sensing of Environment, Volume 193, 2017, Pages 103-126, ISSN 0034-4257,https://doi.org/10.1016/j.rse.2017.02.023.
Fast Vs Slow Variability In Ocean Currents
Ponte, Aurélien (1);
Haro-Gonzalez, Cristina (2);
Autret, Emmanuelle (1);
Yu, Xiaolong (1) - 1: Ifremer, France;
2: CSIC, Spain
Two important contributions to the ocean circulation are slow "balanced" motions and fast (periods less than a day) motions. This co-existence between both types of motions may complicate the estimation and forecast of ocean currents from satellite and in situ observations.
We propose here to compare and contrast:
- the signatures of slow and fast motions on observable variables (e.g. sea level, sea surface temperature, surface currents)
- the dynamics driving each type of motions
These comparisons aim at highlighting which data synergies and methodologies may improve ocean circulation estimates. Leads for relevant efforts in order to achieve the latter objective will finally be presented.
A Synergetic Approach for the Space-Based Sea-Surface Currents Retrieval in the Mediterranean Sea
Ciani, Daniele (1);
Rio, Marie-Hélène (2);
Buongiorno Nardelli, Bruno (3);
Marullo, Salvatore (4);
Menna, Milena (5);
Santoleri, Rosalia (1) - 1: Consiglio Nazionale delle Ricerche, Istituto di Scienze Marine, CNR-ISMAR, Rome, Italy;
2: European Space Agency, ESA-ESRIN, Frascati, Italy;
3: CNR-ISMAR, Naples, Italy;
4: Agenzia Nazionale per le nuove tecnologie, l'energia e lo sviluppo economico sostenibile, ENEA, Frascati, Italy;
5: Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, OGS, Trieste, Italy
The basin scale and synoptic monitoring of the marine currents in the Mediterranean Sea has geophysical, commercial and environmental purposes. At present, this monitoring is achievable via satellite altimetry, allowing to retrieve the large scale ( >= 100 km ) geostrophic component of the surface currents. Nevertheless, the Mediterranean is characterized by Rossby deformation radii around 10-20 km, hence, its typical mesoscale features (O(10-100 km)) are only partially captured by classical satellite altimetry. Moreover, this region (and in particular the Sicily Channel) represents the main ship route between the Indian Ocean and the main harbours of the European Union, hosting 25% of the world oil trade, with a consequent presence of illegal oil spills of the order of 600 Kt per year. This makes high-resolution surface currents a necessary tool for monitoring the Mediterranean Sea and improving the knowledge of its surface dynamics. To this scope, we present a method for the remote retrieval of the sea-surface currents based on the synergy of sea-surface height (SSH) and high-resolution sea-surface temperature (SST) data. During the period 2012-2016, we created daily gap-free high-resolution maps of surface currents at the basin scale. The quality of the new multi-sensor currents has been assessed through comparisons to other surface-currents estimates, as the ones obtained from drifting buoys (at the basin scale), HF-Radar platforms and ocean numerical model outputs in the Malta-Sicily Channel. The study evidenced that our synergetic approach can improve the present-day derivation of the surface currents in the Mediterranean basin, showing satisfying performances even in the reconstruction of the ageostrophic circulation. In the Malta-Sicily Channel, assuming the HF-Radar estimations as a reference, the merged SSH/SST currents exhibit a smaller root mean square error and bias than the altimeter-derived ones, mainly due to their enhanced spatial and temporal resolution. The improvements are also found with respect to the model-derived currents. As a main perspective of this work, we propose to implement our reconstruction method using hourly SST data from geostationary satellites or high resolution ocean colour data. This will bring the remote, basin-scale surface currents retrieval to even higher spatial-temporal resolutions.
High-resolution Currents From The Synergy Between Infrared SST And Altimetry
González-Haro, Cristina (1,2);
Isern-Fontanet, Jordi (1,2);
Tandeo, Pierre (3);
Autret, Emmanuelle (4) - 1: Institut de Ciències del Mar (CSIC), Spain;
2: Barcelona Expert Center BEC,Spain;
3: IMT Atlantique, Labs-STICC,Brest,France;
4: Laboratoire d'Océanographie Physique et Spatiale (LOPS) Ifremer, Plouzané, France
Accurate knowledge of spatial and temporal ocean surface currents at high resolution is essential for both navigation and operational applications. Therefore, a key problem in oceanography is the estimation of the synoptic velocity field. Currently, global ocean surface velocities are routinely estimated from Sea Surface Height (SSH) measurements provided by altimeters. Along-track altimetric measurements of SSH are very well suited to quantify across-track currents, but the spatial resolution of the derived 2D velocities from conventional altimeters is limited to scales above 100-150 km. We present here an approach that takes advantage of the higher temporal and spatial resolution provided by Sea Surface Temperature images (SST). It basically consists on the characterization of a transfer function between SST and SSH that allows to retrieve a synoptic ocean surface current field when applied to a single snapshot of SST.
In this work, we first show that under certain circumstances, the information contained along the tracks may be enough to characterize this transfer function based on model outputs from the Mercator-Ocean system. Then the method is applied to real and simultaneous SST and along track SSH observations provided by ENVISAT and Sentinels 3 satellites. The quality of the method is assessed through comparisons to other surface current estimates, such as HF radar derived currents and in-situ surface currents provided by drifter buoys. The results show the capability to reconstruct the velocity field associated to coastal eddies with diameters of ~10 km.
Synergy Between Altimetry and In-situ Observations to Investigate (Sub)mesoscale Processes
Nencioli, Francesco;
Quartly, Graham - EOSA, Plymouth Marine Laboratory, United Kingdom
Remote sensing and in-situ observations provide complementary information to investigate ocean dynamics. Remote sensing can cover large areas of the ocean on a daily basis over time spans of several years. However, satellite observations are limited to the ocean surface. On the other hand, in-situ observations can provide information on the vertical structure of the water column, but with very localized spatio-temporal extent. More and more studies have focused on synergistic approaches that combine the two types of observations in order to exploit the strength of each individual dataset and, at the same time, minimize their limitations: 3-dimensional in-situ observations can be used to complement and improve the remote sensing ones at the ocean surface; remote sensing observations can be used to contextualize in-situ observations through a broader view of the local dynamical conditions. Both approaches have been particularly successful for the investigation of (sub)mesoscale processes. These includes eddies, fronts and filaments with spatial scales ranging from 10 to 100 km. Such processes are key contributors to the ocean energy balance and to the horizontal transport of tracers, and have a strong influence on biogeochemical and ecological processes. Because of their small spatial scales and ephemeral nature, (sub)mesoscale processes remain an observational challenge for both satellite altimeters and in-situ platforms.
We presents results from a series of studies in which synergistic approaches between altimetry and in-situ platforms have been applied to specifically focus on the investigation of (sub)mesoscale processes in both the coastal and the open ocean. These include: a) the investigation of cross-shelf transport along an ocean front by combining altimetry-based velocity fields and in-situ Lagrangian observations (LATEX project, North-western Mediterranean); b) the retrieval of total geostrophic currents by combining along-track altimetry, in-situ ADCP observations and tracer front directions (GlobCurrent project, South Madagascar); c) the quantification of water transport and exchanges associated with Agulhas rings by combining altimetry-based velocity fields and vertical profiles from Argo floats (South Atlantic). We present the advantages and strengths of each specific approach and discuss its limitations, providing a perspective on the further development of such synergies.
The 25 Year Mesoscale Eddy And FLSE Aviso Atlases
Faugere, Yannice (1);
Delepoulle, Antoine (1);
Guillaume, Taburet (1);
Pujol, Isabelle (1);
Dibarboure, Gerald (2);
Picot, Nicolas (2) - 1: CLS, France;
2: CNES, France
From the gridded altimetry grids, topography and currents, interesting information can be derived using eddy tracking and Lagrangian tools. Integrated in time, the obtained fields allow us to visualize the geophysical content of the altimetry content at finer scales and to colocate it more easily to other sensors such as SST, Ocean Color… Following the reprocessing of the DUACS Sea Level time series in version “DT2018”, a full reprocessing of these value added products has been implemented and is now available on AVISO (https://www.aviso.altimetry.fr/en/data/products/value-added-products.html).
A new “Mesoscale Eddy Trajectory Atlas" has been released in September 2018 on the AVISO altimetry portal. This dataset was produced in collaboration with D. Chelton from Oregon State University, using 25 years of DT2018 daily altimetry maps based on a stable constellation of 2 altimeters (C3S product formely known as AVISO two-sat map). New methods have been developed for this dataset, as a more robust algorithm to track eddies. In addition to the locations of the detected eddies along their trajectories, the atlas includes additional information about the amplitude, rotational speed, radius, eddy type (cyclonic/anticyclonic) and a flag which store missing detection. Additionally, we will operate during 2019 year a software demonstrator to compute and release eddies dataset in near real time with few days delay. This poster will present the methodology and assessment results for these two product lines.
The FSLE maps provides the position, intensity, and orientation of fronts induced by the mesoscale eddies and underlining part of sub-mesoscale transport fronts. They are being increasingly used in physical, biogeochemical, and ecological applications, ranging from real-time support to field studies to co-localisation of animal tracking with Lagrangian Coherent Structures. FLSE products, developed in collaboration with F. d’Ovidio and R. Morrow from LOCEAN and CTOH are now produced operationally and were entirely reprocessed last year, using the CMEMS DT2018 geostrophic current in input.
Geodetic-Based Estimation Of The Geostrophic Currents For Semi-Closed Waterbodies. Case Study: The Red Sea.
Mansi, Ahmed Hamdi (1,2);
Zaki, Ahmed (3,4);
Rabah, Mostafa (5);
El-Fiky, Gamal (3,6) - 1: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Italy;
2: Department of Civil and Environmental Engineering, Politecnico di Milano, Italy;
3: Construction Engineering and Utilities Department, Faculty of Engineering, University of Zaqazig, Egypt;
4: Department of Civil Engineering, Higher Institute of Engineering in El-Shorouk City, Cairo, Egypt;
5: Department of Civil Engineering, Benha Faculty of Engineering, Benha University, Egypt;
6: Higher Institute of Engineering, Belbeis, Egypt
The estimation of sea currents circulation for semi-closed waterbodies is a challenge for GOCE because the spatial scales of their structures are smaller than both these of open ocean and the expected resolution of GOCE models.
An attempt to compute the Sea currents circulation model for the Red implementing the geodetic methods is made. Such a model has been developed exploiting a combination of heterogeneous datasets, i.e., the GOCE-based DIR-R5 and EGM2008 gravity contributions, DTU13 altimetric gravity, Bureau Gravimétrique International (BGI) shipborne gravity observations, and SRTM15_Plus topography data.
In the beginning, the quality of shipborne gravity data, provided by the BGI, has to be assessed, therefore the leave-one-out cross-validation integrated with the Kriging prediction method was chosen to ensure that the shipborne gravity observations are both consistent and gross-errors free. A confidence level of 95.4% was implemented to filter the shipborne data while the cross-validation algorithm was repeatedly applied until the standard deviation (STD) of the residuals, between the observed and estimated gravitational values, are less than 1.5 mGal, which led to the exclusion of about 17.7% of the total shipborne gravity data.
Then, the least-squares collocation (LSC) was implemented to sew the shipborne and the DTU13 gravity data in order to create a unique and consistent gravity field over the Red Sea with no data voids. The combined data were independently tested using a random extraction of a total of 95 shipborne gravity stations. Comparing the extracted shipborne gravity data with the corresponding DTU13 altimetry anomalies, before and after applying the LSC, revealed that significant improvements are achievable using the combined dataset, where the mean value dropped from -3.6 to -0.39 mGal and STD dropped from 9.31 to 2.04 mGal.
At this point, a statistical comparison has to be made between various, i.e., satellite-only and combined, global geopotential models (GGMs) and the shipborne gravity data. Also, the GOCE satellite-only GGMs were evaluated via the spectral analysis and by cross-comparing them to the shipborne free-air gravity anomalies over the Red Sea. On the one side, the EGM2008 combined model manifested the best results with a mean and STD values of 1.35 and 10.11 mGal, respectively. On the other side, the DIR-R5 GOCE-only model synthesized up to degree/order 160 showed the overall best results.
At this point, the Red Sea gravimetric geoid model is computed using the DIR-R5 synthesized up to degree/order 160, EGM2008, and combined gravity dataset (the integrated shipborne observations with DTU13 model). The gravimetric geoid computation methodology is based on the Remove-Compute-Restore technique with residual terrain model (RTM) reduction, and the 1D-FFT technique with Wong-Gore modification.
Finally, the mean dynamic topography (MDT) is simply computed as the difference between the DTU13 mean sea surface (MSS) and the gravimetric geoid. All regions with depth values less than 200 m are excluded and the Gaussian filter with a 1.25o width is used to remove the high-frequency noise that contaminate the final MDT model and accordingly, the geostrophic currents model for the semi-closed Red Sea is estimated.
FSLE Analysis And Validation Of Lagrangian Simulations Based On Satellite-Derived GlobCurrent Velocity Data
Lacorata, Guglielmo (1,2);
Corrado, Raffaele (1);
Falcini, Federico (1);
Santoleri, Rosalia (1) - 1: ISMAR, National Research Council, Rome, Italy.;
2: CETEMPS, Center of Excellence on Remote Sensing and Hydro-Meteorology, L'Aquila, Italy.
We present an independent validation of the satellite surface velocity fields released by the ESA Data User Element GlobCurrent Project. The validation methodology is based on the analysis of Lagrangian numerical trajectories integrated from satellite-based sea surface currents. Two case studies were considered: Mediterranean Sea and North Atlantic Ocean.The Finite-Scale Lyapunov Exponents provide a rigorous, quantitative tool to evaluate Lagrangian simulations with respect to real drifter trajectories. An accuracy threshold scale can be identified as the scale above which the error size, propagating along a numerical trajectory, grows no faster than the relative separation between real drifters. Below this threshold, the error growth rate tends to diverge linearly as the error decreases. The mean error growth speed, at early stage, is found to be related to the kinetic energy of the missing scales of motion, not resolved by the GlobCurrent products. Established kinematic Lagrangian models are, also, exploited to compensate the energy gap between real and numerical trajectories in the unresolved scale range. Ultimately, GlobCurrent surface velocity fields are shown to have overall good Lagrangian skills' for large-scale transport and dispersion numerical simulations.
Mesoscale surface activity in the Eastern Mediterranean: blending Lagrangian drifters with altimetry
Baaklini, Georges (1,3);
Brajard, J. (1);
Issa, L. (2);
Fakhri, M. (3);
Mortier, L. (1) - 1: Sorbonne Université, CNRS-IRD-MNHN, LOCEAN, France;
2: Lebanese American University, Beirut, Lebanon;
3: National Center for Marine Sciences, CNRS-L, Lebanon
Altimetry is a powerful tool for studying the mesoscale surface ocean circulation. However, important errors can arise due to multiple factors such as land contamination, inaccurate tidal and geophysical corrections, inaccurate Mean Dynamic Topography (MDT) and incorrect removal of high frequency atmospheric effects at the sea surface. This is especially the case for the Eastern Mediterranean, which has a complex mesoscale circulation, characterized by permanent and non-permanent eddies and by a relatively small first Rossby radius. The problem in this region is accentuated by the fact that the basin geometry characterized by narrow straits and numerous islands, so the resolution is not sufficient to capture the small details and sharp coastal gradients of the circulation.
Here we try to address this issue by blending Lagrangian drifters with altimetry. We use variational method from which the velocity is corrected by matching observed drifters positions with those predicted by a simple advection model. We take into account the wind effect with imposing a divergence free condition on the velocity correction. The velocity correction is obtained in a time-continuous fashion by assimilating at once an entire trajectory of drifters, using a sliding time window.
When applied to mesoscale eddies detected by altimetry, this method shows that important fine scale features, unresolved in altimetry products can be reconstructed. We are now in the process of validating results. Preliminary results suggest that these novel features match well patterns in SST images and current meters. In the future, we hope to assimilate systematically the Eastern Mediterranean in larger spatio-temporal scale in order to improves the quality of the description of the Mediterranean Sea surface circulation.
15:30 - 16:00
