The core of this presentation explores the inclusion of the promising amplitude compensation and dilation compensation (ACDC) processing in the in-house isardSAT Delay-Doppler chain, exploiting the high-resolution data acquired by Sentinel-3 in the SAR mode over open ocean areas.

ACDC was originally proposed by Chris Ray and isardSAT team within the Sentinel-6 Ground Prototype Processor (GPP) project [Ray2015]. A revisited implementation at stack level [Makhoul2018] is considered in this presentation. The basic idea is to perform a two-step compensation once the stacking has been performed and right after geometry corrections application: 1) along-track amplitude compensation to equalise the Doppler-dependent weighting induced by the acquisition geometry in combination with both antenna and surface radiation patterns; and 2) across-track dilation compensation to correct for the waveform widening when moving away from the central beam. In this way, a better alignment of the waveforms within the stack is obtained by focusing the spread along-track energy into a single range bin, such that an improved speckle reduction and signal-to-noise ratio (SNR) are expected. ACDC provides improvements in the noise retrieval of SSH and specifically in SWH (reduction by a factor of 2) for low SWH when compared to the conventional Delay-Doppler processing [Ray2015,Makhoul2018]. It has been reported [Ray 2018] that retracker bias can be reduced by using a maximum likelihood estimator (MLE) instead of minimizing the mean squared error. This study includes a MLE retracker for comparison, the simple form of the ACDC theoretical waveform means that there is little computational cost to employing a MLE


The performance is analysed in terms of the precision (noise) of retrieved geophysical parameters and compared to the conventional Delay-Doppler processing, using directly nominal Sentinel-3 L2 data.

References:
[Ray2015] Ray, Chris, Mònica Roca, Cristina Martin-Puig, Roger Escolà, and Albert Garcia. "Amplitude and dilation compensation of the SAR altimeter backscattered power." IEEE Geoscience and Remote Sensing Letters 12, no. 12 (2015): 2473-2476.

[Makhoul2018] Makhoul, Eduardo, Mònica Roca, Chris Ray, Roger Escolà, and Albert Garcia-Mondéjar. "Evaluation of the precision of different Delay-Doppler Processor (DDP) algorithms using CryoSat-2 data over open ocean." Advances in Space Research 62, no. 6 (2018): 1464-1478.

[Ray2018] Ray, Chris, Mònica Roca, Eduardo Makhoul, “Evaluation of retracker bias due to waveform fitting method”, Ocean Surface Topography Science Team Meeting, October 2018.

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The Nordic Seas is a buffer zone between the warm and saline North Atlantic and the cold and fresh Arctic Ocean. The poleward transport of the warm Atlantic Water via the Norwegian Sea situated in the eastern Nordic Seas is a key component in maintaining a relatively mild climate in the northwestern Europe, and has been subject to investigations since the Norwegian North-Atlantic Expedition during 1876-1878 (Mohn and Wille, 1882). Atlantic Water is transported poleward by the Norwegian Atlantic Current which is a two-branch current system, of which the eastern branch follows the shelf edge as a barotropic slope current, while the western branch is considered to be a topographically guided jet current. By the end of the last decade studies using RAFOS floats and surface drifters indicated the presence of interaction or crossover flows between the two branches which contradict the former concept of the two branches as separate flows. However, identification of the main locations of crossover flows, its temporal variability, influence of atmospheric forcing and the possible impacts on the downstream transports of heat, salt and volume have not been adequately assessed.

For the first time, using synergy of multi-variable satellite observations, we attempt to study the crossover flows between the two branches of the Norwegian Atlantic Current. Analysis performed during the altimeter time period (1993-2017) is based on the geostrophic and total surface currents obtained from the ESA´s GlobCurrent project. Locations and magnitude of the crossover flows detected from altimeter data has been validated using SAR doppler derived mean surface velocities. In addition, its seasonal and inter-annual variability is examined. The role of eddies in facilitating the crossover flows is examined using high-resolution along track altimeter data, and also by applying an eddy detecting algorithm on gridded sea level data. Furthermore, the impact of the three main modes of the atmospheric circulation in the Norwegian Sea on the variability of the crossover flows is also investigated.

The preliminary results of this study imply that the crossover of Atlantic Water from the western to the eastern branch may be more important for the climate of the Barents Sea and Arctic Ocean than previously assumed.

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Sea level change is a highly important indicator of climate change. This change is an integrated response of several components of the Earth system (ocean, atmosphere, cryosphere and hydrosphere) to natural and anthropogenic forcing. Studies of the sea level budget help to explain observed sea level changes, and better understand the temporal and spatial scales of the dominant processes of individual components. Furthermore, it advances the quantitative understanding of uncertainties, which, in turn, allows us to place bounds on poorly known contributions (e.g., ocean warming below 2000 m and freshwater discharge), none of which are adequately measured by current observing systems. This is also highly valuable for validation of climate models.

The ESA Sea Level Budget Closure study (SLBC_cci) is a cross-Essential Climate Variable (ECV) project that aims to close the sea level budget of the Global Ocean as well as for the regional Arctic Ocean. The Arctic sea level budget is of interest as the region has warmed at a rate about twice the rest of the globe during recent decades. As such, both the thermal ocean expansion and the redistribution of the melting water from glaciers and polar ice sheets into the ocean are contributing to an Arctic sea level rise that needs to be properly quantified.

The closure of the Arctic sea level budget implies that the observed changes of mean sea level as determined from satellite altimetry equal the sum of observed changes in ocean mass and the steric component. The ocean mass changes are derived from the GRACE satellite gravimetry (since 2002) and from individual contributions from melting glaciers and ice sheets, changes in land water storage (including snow cover) and atmospheric water content. Estimates of steric sea level are obtained from in situ ocean temperature and salinity measurements.

We report the results of the Arctic sea level budget assessment estimated using the latest release (version 2) of the datasets determined in the project, the focus on two specific time periods: 1993-2016 (the altimetry period) and 2003-2016 (the GRACE/Argo period).

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Sea surface temperature is a key parameter that influences many environmental processes, including ocean dynamics, biology and climate. Thermal gradients at the upper ocean are directly relatable with the heat budget between the ocean and atmosphere which has a crucial role in the global climate. The accurate knowledge of SST regarding not only its variability, but its short- and long-time trends is imperative to understand the ocean’s role on a changing climate. Good assessment of the SST across the Atlantic is essential to understand the ocean’s contribution to climate change and will contribute for the effectiveness of protective and preventive initiatives across the Europe, rendering this study directly aligned with at least two Sustainable Development Goals (Life below Water and Climate Action) of the UN 2030 Agenda [1].
Here, the European Space Agency’s Sea Surface Temperature Climate Change Initiative (ESA SST CCI) product is validated using in-situ SST data collected in the eastern Atlantic. The main objective of this study is to show the applicability of the CCI data for climate studies over the Atlantic, and in particular over the coastal ocean, where the buoys are moored.
The ESA SST CCI dataset used in this study is the ESA SST CCI Analysis LT product version 1.0 [2] which consists of daily maps of the sea surface temperature (at 0.2 m) spanning over the period between 1991 and 2010. Daily values of SST from the ESA SST CCI product were compared against in-situ data acquired by thermistors located at 0.7 m depth, from 11 coastal buoys operated by the Hydrographic Institute (Instituto Hidrográfico), the University of Azores (Universidade dos Açores), Observatory for the Environment of the Azores, and the Ports Administration of the Madeira Autonomous Region (Administração dos Portos da Região Autónoma da Madeira), providing a significant coverage across the eastern Atlantic, in an area of relatively scarce in situ data.
The statistical relationship between daily ESA SST CCI retrievals and in-situ data will be analyzed as well as uncertainties associated with pixel match-ups and sensitivity of the results for different match-up techniques. The potential of using in-situ data from coastal moored buoys to assess ESA SST CCI datasets and how climate studies across the Atlantic could benefit from the integrative use of in situ and satellite retrievals will be discussed.

References:
[1] UN General Assembly, Transforming our world: the 2030 Agenda for Sustainable Development, 21 October 2015, A/RES/70/1
[2] Merchant, C. J., Embury, O., Roberts-Jones, J., Fiedler, E., Bulgin, C. E., Corlett, G. K., Good, S., McLaren, A., Rayner, N., Morak-Bozzo, S. and Donlon, C. (2014), Sea surface temperature datasets for climate applications from Phase 1 of the European Space Agency Climate Change Initiative (SST CCI). Geoscience Data Journal, 1: 179–191. doi: 10.1002/gdj3.20

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The DUACS system (Data Unification and Altimeter Combination System) produces, as part of the CNES/SALP project, and the Copernicus Marine Environment and Monitoring Service, high quality multimission altimetry Sea Level products for oceanographic applications, climate forecasting centers, geophysic and biology communities... These products consist in directly usable and easy to manipulate Level 3 (along-track cross-calibrated SLA) and Level 4 products (multiple sensors merged as maps or time series) and are available in global and regional version (Mediterranean Sea, Arctic, European Shelves …).

The system today merges data from 5 satellites (Jason-3, Sentinel-3A, Jason-2, Altika, and Cryosat-2) and soon 6 with Sentinel-3B. This high number of altimeter missions will contribute to the robustness of the system and the product quality, but also opens new perspectives in terms of resolution. Using the global Synthetic Aperture Radar mode (SARM) coverage of the Sentinel-3 constellation A with innovative processing (LR-RMC), and reducing the LRM altimeters (retracking, editing, noise reduction...) will allow us to fully exploit the fine-scale content of the altimetric mission. Thanks to this increase of altimetry observations we are now able to improve Level-4 products by combining these new Level-3 products and new mapping methodology, such as dynamic interpolation. Finally these improvements benefit to downstream products : geostrophic currents, Lagrangian products, eddy atlas….

For 3 years 2016-2019, R&D studies have been implemented by CLS and CNES team. The highlights of these studies will be presented here and the final set of demo samples produced will be also described. Finally, the transition plan to operation in CMEMS will be discussed.

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Since June 2018 the Copernicus Marine Environment and monitoring Services (CMEMS) is delivering a new ocean surface current product that addresses numerous marine applications. This product based on observation-based approach is complementary to ocean current estimates provided by modelling/assimilation systems. It consists in surface and 15m depth total current estimates based on the merging of satellite and in situ observations. The operational product delivered through the CMEMS is an heritage from different R&D initiatives as the GlobCurrent project from the European Space Agency (ESA) and CNES mean dynamic topography studies. They are now available in Near-Real-Time (NRT) from January the 5th of 2017 to present days and as Multi-Year Products (MYP) for the past 25 years. They are distributed through the CMEMS catalogue (http://marine.copernicus.eu/services-portfolio) as part of the Muli-Observation TAC (thematic Assembly Center).

The currents are estimated as the sum of the geostrophic and Ekman components. The geostrophic current is based on the altimeter velocity maps and the mean geostrophic velocities derived from the CNES-CLS13 Mean Dynamic Topography. The Multi-Year Products use the DUACS2014 version of the geostrophy (Pujol et al, 2016), while the NRT products are up to date with the last version of the CMEMS geostrophic products (DUACS2018, Taburet et al, 2018)
Ekman currents at two levels (surface and 15m) are calculated from an empirical model based on Rio et al (2014) methodology and ECMWF wind stress (NRT and multi-year fields). The model parameters (amplitude and angle from the wind direction) have been derived as to minimize the misfit between wind stress data and the ageostrophic component extracted from in-situ drifter velocities. The SVP drifters at 15m depth from the reprocessed AOML database and velocity derived from the Argo floats at the surface have been used. Parameters have been fitted by month, longitude and latitude. They feature a clear seasonal cycle in good agreement with the ocean stratification variability. Also, the surface and 15m Ekman currents show a spiral-like response to wind stress in good qualitative agreement with the theory.

Currents have been calculated over a 25 years period (1993-2018). Surface (15m) currents are validated against surface ARGO (15m drogued SVP drifters) velocity. The estimated error features an important spatial variability, with an increase at the equator and in coastal area. A time dependence is also found, due to the evolution of the altimetric mission constellation (shorter scales of the ocean dynamics will be resolved with increasing number of simultaneously flying altimeters) and the varying in situ data spatial coverage (time varying number of drifters.)
The CMEMS MULTIOBS currents have also been compared to similar products as the Ocean Surface Current Analyses Real-time (OSCAR, Bonjean and Lagerlorf, 2002) and show better consistency with 15m SVP drifters than OSCAR.
Further improvements of the method are in progress, focusing on Ekman model improvement to take into account the Mixed Layer Depth information. Some results of this new version of the products will be presented and seasonal variability of the two versions will be discussed.

Rio, M.-H., S. Mulet, and N. Picot, 2014: Beyond GOCE for the ocean circulation estimate: Synergetic use of altimetry, gravimetry, and in situ data provides new insight into geostrophic and Ekman currents, Geophys. Res. Lett., 41, doi:10.1002/2014GL061773.

Bonjean, F., G.S.E. Lagerloef, 2002 : Diagnostic model and anlysis of the surface currents in the Tropical Pacific Ocean. J. Phys. Oceanogr., 32, 2938-2954.
Pujol, M-I., Y. Faugère, G. Taburet, S. Dupuy, C. Pelloquin, M. Ablain, and N. Picot, 2016: DUACS DT2014: The new multi-mission altimeter dataset reprocessed over 20 years. Ocean Sci., 2, 1067–1090, doi:10.5194/os-12-1067-2016.

Taburet, G, SL-TAC team, 2018 : CMEMS-SL-QUID-008-032-051: http://marine.copernicus.eu/documents/QUID/CMEMS-SL-QUID-008-032-051.pdf

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Atlantic waters are the main source of oceanic heat and salt flux to the Arctic. On the way from the Nordic Seas to the Arctic Ocean, warm and saline Atlantic Water change properties of the surrounding waters masses, affect ice extent and the rate of deep water formation. Variations of properties of the Atlantic Water change ocean-atmosphere heat exchange and have a significant effect on the local climate.
In this research we investigate seasonal and inter-annual variations of the advective heat fluxes in the main branches of the Atlantic Water, their transformation as they move northward from Svinoy section to the northern part of the Fram Strait. Link between the oceanic heat fluxes with indices of atmospheric circulation (AO, NAO, indices of zonal and meridional transport) and with AMO ocean index are investigated. Heat fluxes were calculated as:
Q= ρ*Cp*(T-Tref )*v*dx*dz, where ρ-water density; Cp – specific heat capacity for water; Tref – reference temperature (-1.8°C); T – water temperature; v – current velocity perpendicular to the section; dx – distance between two stations, dz – layer thickness.
For the study of oceanic processes, an ARMOR3D dataset (E.U. Copernicus Marine Service Information) was used. ARMOR3D is an observation based product that combines two types of data: satellite SLA, SST, SSS datasets and in-situ T, S vertical profiles. The data-set presents a global 3D monthly temperature, salinity and geostrophic velocities fields at a regular grid with the spatial resolution of 0.25°x0.25°.
The heat fluxes from ARMOR3D dataset were validated against those derived from moorings in the Fram Strait deployed by AWI. The comparison showed that ARMOR3D has a somewhat lower annual variability, but reproduces the main seasonal and inter-annual variability with a sufficient accuracy in the upper 500-m layer. The accuracy of the reanalysis decreases with increasing depth and in the areas partly covered with sea ice. However, as the study region represents upper layers of the ice-free area of the Nordic Seas, ARMOR3D data-set was considered to be suited for the current study. The resulting advective heat fluxes through all selected sections across the eastern part of the Nordic Seas demonstrated a strong seasonality with maximum in winter time (December-January) and minimum in summer (June – July). No significant long-term trends were found in the heat fluxes time series. Correlations between the heat fluxes at different sections decrease to the north, which indicates a significant role of water dynamics and of ocean-atmosphere exchange in the Nordic Seas in interannual variations of the heat coming to the Arctic.
The research was supported by RSF (project No. 17-17-01151 )

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This work is devoted to the processing and analysis of Baltic Sea remote sensing data. Processing and analysis of the ocean data is carried out using modern data processing technologies. Changes of the hydro-physical parameters of the Baltic Sea are discussed in the work.

The work is based on the Copernicus Marine Environment Monitoring Service (http://marine.copernicus.eu/) data. Data on the Sea surface temperature (SST) from the following satellites are used in the work: NOAA AVHRRs, Envisat ATSR1, ATSR2 and AATSR, Terra MODIS, Aqua MODIS, MSG Seviri (product ID SST_Bal_sst_L4_rep_observations_010_016 for 1982-2011 years, product ID SST_ Bal_sst_L4_nrt_ observations_010_007_b for 2011-2018 years).
Two modern programming languages were used to process this data – Python and R. Python — high-level, general-purpose, performance-oriented programming language. The language is distinguished by its convenient syntax and ease of use, it allows one to quickly work and integrate different software components into a single system. In the Python programming language, a program is implemented that allows one to receive data on the SST from a resource, and write to files of the required type. The daily data on the SST of the Baltic Sea for the years 1982-2018 were processed using the implemented set of scripts. The use of the Python language is convenient for solving problems of receiving and processing data, as well as for integrating the codes of various applications.
For data analysis, a programming language R was used. The language was developed by scientists mainly for statistical data processing and is freely distributed. R supports a wide range of statistical and numerical methods, data visualization is conveniently implemented. Using the R language allows one to efficiently analyze data, emphasize structures and anomalies in data sets, identify and investigate regularities using statistical methods. An analysis on the Baltic SST data for 1982–2018 years was made using the capabilities of the R language.
The data analysis allows to highlight the positive trend in changing values of the Baltic SST. This suggests the warming of the Baltic Sea in recent decades. A positive trend was noted in the similar works of other scientists (e.g. Lebedev, 2014; Schuckmann et al., 2018), this study confirms that the trend for the whole sea is being preserved. The spatial variability of the Baltic SST is also discussed in the work. The warming of the Gulf of Finland is no longer so rapid, although it exceeds the average warming rate of the whole sea.

The work was supported by the grant of the president of the Russian Federation №МК-3228.2018.5.

References
Lutz, М. Programming in Python. V. 1 / М. Lutz. - Moscow: Simbol. - 2016. - 992 p. (in Russian)
R Core Team (2018) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. (https://www.R-project.org/)
Lebedev S.A. Climatic changes in surface temperature and the level of the Baltic Sea according to remote sensing data // Amber Bridge. Journal of Regional Studies. - 2014. - № 1 (1). - P.78–95. (in Russian)
Karina von Schuckmann, Pierre-Yves Le Traon, Neville Smith (Chair), Ananda Pascual, Pierre Brasseur, Katja Fennel & Samy Djavidnia (2018) Copernicus Marine Service Ocean State Report, Journal of Operational Oceanography, 11:sup1, S1-S142.

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Satellite-derived sea surface temperature (SST) trends are built at the cell scale to investigate long-term changes in oceanic patterns. The analysis is applied to the Canary Current Upwelling System (CCUS) one of eastern boundary of oceans, from 10º to 45º N, because the strong dynamic link between the atmosphere and the ocean makes upwelling regions highly sensitive to global change and ideal to monitor and investigate its effects. Monthly mean SST data with a resolution of 4x4 km, extending from 1982 to 2014, are derived from the AVHRR Pathfinder SST Version 5.2 and Version 5.3 dataset. A brief synopsis was also done with the MODIS Terra and Aqua satellite datasets, although with a smaller time length than the AVHRR Pathfinder dataset. Only the highest quality cell satellite data are retained for this investigation, leaving voids on the temperature grid nodes corresponding to the rejected values. Since the voids are mainly originated by the cloud cover and fogs, strongly affected by the seasonality, we described several procedures to fill these data gaps that guarantee that annual and seasonal averages are not biased towards the more represented season in the SST data.
The obtained fields of SST trends show an overall warming trend in the CCUS. In the northern segment of CCUS, the Iberian Upwelling System (IUS), this warming trend weakens since the 1990s and since the 2000s in the southern segment, the African Upwelling System (AUS). At the AUS is observed a cooling trend south Cape Blanc and Cape Vert. Although a small period for long-term analyses, during the last five years (2010-2014) of the time-series the obtained linear trends makes reference of a stronger cooling trend in the entire CCUS coastal region below the 39ºN and in the AUS region below 25ºN. Meanwhile in the remaining CCUS region a generalized warming trend still endures since the first years. However, alternate patches of significantly different warming rates are observed, ranging from large scale down to mesoscale. Known coastal upwelling features are seen to warm at a lower rate than corresponding offshore waters, pointing to an intensification of the upwelling in the last decades. Our results evidence the main role that mesoscale processes play in the modulation of the spatial and temporal variability of SST, namely at the decadal scale. This result prevents any global conclusion about the relaxation or intensification of the upwelling at the scale of the entire CCUS. The detail in the warming variability obtained here results in a large extent from the fine scale analysis and the numerical processing carefully designed to avoid trend bias in the climatological studies.
This work was conducted in the frame of "LongUp - Long Term Variability of the Canary Current Upwelling System" project (PTDC/AAC-CLI/105296/2008) and a PhD research grant (SFRH/BD/84666/2012) funded by Fundação para a Ciência e Tecnologia (FCT). This study is a contribution to FCT funded project UID/Multi/04326/2019.

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Geoid models from recent satellite gravity missions, such as GOCE and GRACE, in combination with sea surface models from satellite altimetry, allow obtaining a mean dynamic ocean topography (MDT) with rather high spatial resolution and accuracy. In particular, the European Space Agency mission GOCE (Gravity field and steady-state Ocean Circulation Explorer), directly observing the second derivatives of the gravitational potential, provides stationary global geoid models with an accuracy of 1-2 cm at a resolution of about 100 km, well compatible with oceanographic studies.
The MDT computation implies a combination of data with fundamentally different characteristics and different spatial resolutions. Spectral consistency implies the removal of the short-scale features from the altimetric sea surface height by applying a proper filtering procedure, so to provide altimetric data consistent with the resolution of the satellite-only geoid model. In particular, the Mediterranean Sea represents a challenging basin for the exploitation of GOCE data because the mean circulation is characterized by scales shorter than 100 km, thus smaller than the spatial resolution of the satellite observations. Furthermore, the MDT signal variability is much lower than in open oceans. For these reasons, suitable filtering techniques are necessary.
The goal of this work is to compute an MDT, and the corresponding geostrophic circulation, for the Mediterranean Sea based on a GOCE-only geoid model. In this respect, the target of the study is not the computation of the most informative Mediterranean MDT, requiring combinations with other models and data sources, but the assessment of the actual contribution of the GOCE mission to the basin geostrophic circulation. This is done by applying an optimal filtering strategy, based on least-squares collocation, locally adapting the signal and error covariance functions to the Mediterranean Sea characteristics. The estimated quantities are provided with the corresponding error estimates by exploiting the collocation theory. This allows setting up suitable statistical tests to detect the circulation patterns that are significantly visible by GOCE.
This study has been performed in the framework of the STSE-ESA MEGG-C project.

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The difference between the sea surface height (SSH) above a reference ellipsoid and the geoid is the ocean's dynamic topography (DOT). It reflects many characteristics of the ocean circulation. Although the DOT is time-variable, the focus is often on its steady-state part, called the mean dynamic ocean topography (MDT). The geodetic estimation of the DOT (or MDT) is typically based on the separation of (mean) altimetric SSH measurements into the MDT and the geoid. For the separation process, additional independent information about the geoid, the MDT or both is required. When omitting any kind of oceanographic input data (ocean salinity, temperature, pressure), instead relying only on satellite derived geoid and SSH data, the resulting MDT estimate is called 'geodetic'. A remaining scientific issue is the spectral inconsistency of the involved data sets.
Typical approaches for (geodetic) DOT or MDT estimation from altimetric measurements and geoid information at the global or regional scale start by actually computing differences between a gridded mean sea surface (MSS) data set and geoid information from a satellite based model. Different kinds of filters are applied to homogenize the data sets and account for their spectral inconsistency. Often a simple Gaussian low-pass filter is applied to the difference in spatial domain to derive a gridded MDT. Stochastic information on the accuracy of the geoid and the MSS are not accounted for.
In contrast to the well established multi-step procedure, we propose a parametric representation of the MDT in an integrated (one step) approach. A finite element approach on a triangulation of the region of interest is used to parameterize the MDT continuously. Depending on the actually chosen finite element, different signal characteristics can be represented (smoothness, filtering) by the model.
In this contribution we will demonstrate that a parametric finite element based model is well suited to represent the signal of the MDT within a region of interest. We will focus on a triangulation which is well suited to cover the ocean areas. Furthermore, we concentrate on finite elements which are able to represent a signal either C0-smooth (linear elements) or C1-smooth (e.g. ARGYRIS element). We will show that such parametric models can be easily used for the estimation of geodetic MDTs, as due to the parametric nature, observation equations can be set up at the actual measurement location. Additionally, different observation equations for various functionals sensitive to the MDT signal - like along-track satellite altimetry, radial SAR derived surface velocities or velocities derived by surface drifters - can be formulated. We will summarize the status of the DFG funded project PARASURV, where an integrated approach of finite element based MDT estimation will be developed (with a special focus on the use of radial SAR derived surface velocities).

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This presentation describes the results of the Living Planet ESA Fellowship (2015-2018) postdoctoral project, which main aim was to reconstruct 3D currents along the West Spitsbergen Current (72°N-80°N) in 2000-
2012 using a combination of in situ measurements, satellite altimetry and a numerical model.
Three in situ data sets were used:
i)the in situ data consisted of CTD cruise data measured every July,ii)long-term moored instruments of currents in the Fram Strait at 78.83°N, 5-8.6°E and iii) 1 year of moored current profiles measured by MMP instrument at 78.43°N, 9.19°E between September 2009-September 2010.
For the reconstruction of WSC, daily currents, calculated from ADT and SLA measured by satellite altimeters, gathered as L4 gridded product of CMEMS, were used. The modelled output variables were first validated against all the used observations. Because the agreement of the modelled currents and other validated fields with the observations was found to be satisfactory, the model structure function and the mean modelled currents were used in the current reconstruction.
Due to substantial differences in the mean surface currents between the modelled and satellite-derived currents in the Fram Strait two methods of the reconstruction were proposed. Method 1 is the original method that uses the absolute surface geostrophic currents derived from the satellite altimetry, that are a combination of the mean and time-variable currents, and the vertical structure function that was obtained from the numerical model for the 0.25°x0.25°grid between water depths of 500-2000m. The 2nd method is an upgrade of the 1st method, for the 2nd method, the mean circulation was taken form the numerical model, and its variable part was obtained from the combination of the surface geostrophic currents derived from SLA measured by satellite altimeters and a vertical structure function extracted from the model as the mean correlation
coefficients in 2000-2012, and mean modelled currents. The two methods of WSC reconstruction differ only by the mean currents used for the reconstruction. Considering the flow of WSC along depth contours between 500 and 2000m along 72°N-80°N the greatest differences between the two Methods were found in the Fram Strait, mainly due to differences in the modelled and satellite-derived mean currents. The mean currents derived using MDT measured by satellite altimetry in the Fram Strait was 50% of the mean observed values.

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Teleconnections are climate links between regions as far apart as thousands of kilometres. The origin of teleconnections are low-frequency and large-scale persistent and recurrent patterns of atmospheric pressure and circulation anomalies, known as teleconnection patterns (TP). The configurations and phases of the TP are currently well known, as well as their associated temperature and precipitation patterns. TP are responsible for the variability occurring on several fields that in turn change the oceanic conditions and sea level, namely sea level pressure (SLP), sea surface temperature (SST), and wind. As a consequence, TP are expected to produce strong sea level variability and inter-annual fluctuations in the rates of sea level rise, however the sea level anomaly (SLA) response to these patterns has not been fully analysed yet. Being the SLA a valuable proxy for detecting long-term changes of the global ocean, as well as short-term and annual variations, this study aims at understanding the SLA response to the North Atlantic main modes of variability over the north Atlantic Ocean and several semi-enclosed seas, therefore, filling some gaps in existing knowledge.
The amplitude and phase of the TP are given by a time-series defined by tropospheric pressure and/or sea surface temperature (SST) variations, known as the TP index. The indices of those TP possessing their anomaly centres located over the North Atlantic Ocean or Eurasia – North Atlantic Oscillation (NAO), East Atlantic (EA), East Atlantic/Western Russia (EA/WR), Scandinavia (SCAND), Polar/Eurasia (POL), Tropical Northern/Southern Atlantic (TNA) – have been analyzed in this study. TP are generally characterized by monthly and seasonal data, as these are the key scales to analyze the atmosphere-ocean interaction.
A methodology able to provide results for a better understanding of the observed SLA changes occurring in response to the TP and the atmosphere-ocean links that contribute to these changes was developed. In the first place, correlation maps between each TP and SLA were generated for each climatological season. Data used were V2.0 SLA monthly grids from the European Space Agency (ESA) Sea Level Climate Change Initiative (SL-cci) and timeseries of monthly TP indices from NOAA’s Climate Prediction Center. The study period ranges from 1993 to 2015. Secondly, composite maps of SST, SLP and wind stress were also computed during the positive and negative phases of each index and for each climatological season, representing their mean state during these periods. The study region encompasses both the tropical and extratropical Northeast Atlantic, the Iberia-Biscay-Irish region and the semi-enclosed North, Baltic, Mediterranean and Black seas.
The intercomparison of the results from both steps allow to conclude the existence of significant correlation between SLA and most of the analysed TP. Both the seasons and the geographic areas with the most significant correlations have been identified. As expected, the correlation with NAO has the highest spatial extend over the study region, including all the semi-enclosed seas, during boreal winter. However other regions show significant correlations with other TP. For example, results show that the SLA in the Baltic Sea is negatively correlated with the SCAND index throughout the year, whereas EA/WR index affects mainly the Atlantic Ocean northwards of 50°N, in summer and winter, and SLA and POL correlations are found in the Black Sea during spring and summer. Also, significant correlations have been found over the tropical Atlantic, related with the mean positions of the North Equatorial Current and Counter-Current. These SLA-TP correlations reveal an important oceanic forcing of the atmosphere and, since the physical processes underlying SLA-TP correlations were also investigated, a better understanding of the basin-scale observed SLA changes and atmosphere-ocean links has been made possible.

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Thanks to its current accuracy and maturity, altimetry is considered as a fully operational observing system dedicated to various applications such as climate studies. Altimeter measurements are corrected from several geophysical parameters in order to isolate the oceanic variability and the tide correction is one of the most important. The accuracy of tidal models has been much improved for last 25 years leading to centimetric accuracy in open ocean.

The last version of the global tidal model FES2014b, developed a few years ago, took advantage of long altimeter time series, better altimeter standards (instrumental and geophysical corrections, orbits), improved modelling and data assimilation techniques. The grid resolution has been increased in areas of interest like shallow waters and on the slope of the continental shelves. The error of the pure hydrodynamic ocean model has been divided by a factor of 2 compared to previous version. A specific loading tide solution is also proposed in coherency with FES2014b ocean solution. FES2014b validation results showed a significant improvement particularly in shallow waters and in some parts of the Arctic region, compared to other global tidal models available (GOT4v10, DTU10, TPXO8).
However some errors still remain mainly in some shallow waters and in polar regions, due to the omission of compound tides, to remaining bathymetric errors, to sea ice effects which are not entirely taken into account ...
Today the new challenges of the tide correction for HR altimetry include even higher resolution in coastal areas, extending the tidal spectrum and keeping improving the hydrodynamic modelling and the bathymetry accuracy; polar tides remains also a challenge with the use of recent altimeters like Cryosat-2 or Saral/AltiKa which samples these high latitudes regions. We present the perspectives of improvement of the new global tidal solution FES2020 and some preliminary impact studies done in preparation of this new tide model version.

Area C - Board 347

Starting from the first long-term mission of Topex/Poseidon in the early 90s, and thanks to a constant monitoring of ocean surface topography over the last two decades, the ocean has kept revealing its turbulent aspects in ever-greater detail. A rich variety of dynamic regimes at mesoscale level have emerged so far, that are still poorly reproduced by global modelling studies due to coarse resolution (although exceptions at eddying resolution are present, see for example Chassignet. et al, 2014), inaccurate bathymetry, poor parametrizations etc. Moreover, next-generation satellite SWOT mission is designed to go further, investigating mesoscale/sub-mesocale structures that could be resolved spatially, and even temporally whether coupled with current conventional altimetry data (Pujol et al., 2012).

While it is true that eddy-permitting simulations do not resolve most of such surface variability, the corresponding reanalyses seem to be able to sustain it once the SLA measurements are assimilated. Moreover, deep discrete structures appear in this case, generated by baroclinic corrections to the water column from SLA assimilation that are consistently dragged/advected/diffused by the model primitive equations.

In this work, we focus on such added value of SLA assimilation that is able to generate “realistic” three-dimensional discrete variability in reanalysis dataset. We compare the 3D eddy content and energetics of three different datasets: a global ocean reanalysis, a free global ocean simulation and an observation-based dataset used as an independent benchmark where no ocean general circulation model has been applied. Datasets are at 1/4 horizontal resolution and cover a 10-year period.

While the free simulation fairly reproduces eddies emerging from western boundary currents and deep baroclinic instabilities, it underestimates shallower vortexes. The ocean reanalysis recovers most of the missing turbulence that is not generated by the model itself and consistently projects surface variability through the full water column. Eddies are responsible for more than 60% of total EKE in regions where deep baroclinic instabilities occur and where eddy cores are shown to be located well-below the ocean surface.
A global 3D eddy detection system is used to bypass the need of regional-dependent definition of thresholds. It provides full three-dimensional eddy structures segmenting vertical profiles from local rotational velocities. This criterion is crucial for discerning real eddies from transient surface noise. Eddy thickness is also compared, and eddies in the reanalysis dataset are found to be shallower than in the observation-based dataset (Cipollone et al. 2017).

A further result of our analysis shows that about the 10% of surface variability generated by SLA assimilation remains superficial without a deep vortex associated to it. This can be seen as a first attempt to estimate the fraction of SLA measurements that effectively generates realistic structures compatible with a general circulation model.

Chassignet, E.P., J.G. Richman, E.J. Metzger, X. Xu, P.G. Hogan, B.K. Arbic, and A.J. Wallcraft, 2014,CLIVAR Exchanges, 19(2), 30-33

Pujol, M.-I., Dibarboure, G., Traon, P.-Y. L., and Klein, P.,2012, Using High-Resolution Altimetry to Observe Mesoscale Signals, Journal of Atmospheric and Oceanic Technology, 29, 1409–1416

Cipollone, A., Masina, S., Storto, A. and Iovino, D. , 2017, Benchmarking the mesoscale variability in global ocean eddy-permitting numerical systems, Ocean Dynamics 67: 1313

Area C - Board 348

Satellite altimetry today provides exceptional means for absolute and undisputable monitoring of changes in sea level and inland waters (rivers and lakes), over regional to global scales, with accuracies of [mm/yr] and with respect to the center of mass of the Earth. Altimetry also measures wind speed on sea surface, sea state, determines ocean circulation, bathymetry, but also monitors melting rates of ice sheets in Arctic, Antarctica, and the Himalayas and observes the amounts of the sea ice and freeboard; All these with an accuracy less than 1cm from an attitude of 800-1300 km above the earth’s surface.

To continue doing that, altimetry system’s responses have to be continuously monitored and controlled for their quality, biases, errors, drifts, etc. Relations among different missions have to be established on a common and reliable earth-center reference system, maintained for a long period of time (at least 20 years).

At this stage, it is high time to (1) Build upon commonly adopted procedures, protocols and uncertainty for Cal/Val, (2) Provide control and checks for monitoring altimeter degradation as fast as possible, (3) Connect one altimetry mission with another, seamlessly and smoothly, (4) Adopt a stable framework for international and interdisciplinary cooperation, (5) Allow data integration between different scientific fields and disciplines, (6) Set standards for measurements and results between various Cal/Val facilities, (7) Ensure Cal/Val procedures, results are well documented and traceable to SI units, (8) Provide transparent protocols and best practices for establishing new Cal/Val sites and finally, dissipate responsibility to end user to decide the extent of fit for his requirements.

This presentation generates a summary roadmap to be used by all satellite altimetry Cal/Val community to (1) support accuracy in scientific and monitoring data we produce and evaluate, (2) to provide accurate information presented to the Public for understanding effects of sea level rise to their lives, and finally (3) to help make the right decisions, and put into action the right Policies for climate change. Ways to express uncertainty will be given to meet the standard of Fiducial Reference Measurements but also provide SI-traceable (Système International d'Unités) calibration results.

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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 new 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.

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The circulation of the Western Mediterranean Sea (WMED) is characterized by the presence of an intense mesoscale activity. The Algerian Current flows along the entire southern boundary of the basin and is usually associated to the formation and propagation of cyclonic and anticyclonic eddies detaching from the main flow and propagating in the WMED.
Main properties of mesoscale eddies, like track, lifetime and associated values of Sea Level Anomaly are usually studied through altimetry data, while in situ data collected through CTD casts or unmanned marine vehicles are rare.
In this study, we used the outputs of an automated detection and tracking hybrid method applied to 24 years of sea level anomaly data over the WMED. The altimetry data used are the merged, delayed-time gridded maps of optimally interpolated SLA, now distributed by the Copernicus Marine Environment Monitoring Service (CMEMS). In order to study the connectivity due to eddies among different WMED sub-regions, we carried on a set of lagrangian statistics analyses applied to eddy tracks. The connections due to the eddies among 21 sub-regions of the WMED are studied by looking at the statistical properties of the eddy trajectories obtained with the tracking algorithm. In particular, we computed the transit time for each sub-region, a pseudo-Eulerian statistics and the probabilities of connection among the sub-regions.
The sub-regions are distributed on a 2°x2° regular longitude/latitude grid over the whole WMED.
Different results are obtained for cyclonic and anticyclonic eddies, highlighting similarities as well as expected differences between the two groups.
The combination of an eddy detection and tracking method with a statistical connectivity analysis allowed a further study of the connections between different areas of the basin. The importance of this study is also related to the eddy ability to transport heat, salt, oxygen, nutrients and other properties during their lifetime preserving the involved water masses from the mixing with the surrounding water.

Area C - Board 351

The Lofoten Basin is one of the most dynamically unstable regions of the North Atlantic and represents a ‘hot spot’ of the mesoscale eddy activity in the Nordic Seas. A quasi-stationary, deep, anticyclonic eddy is located in the central part of the basin. One of the key features of the Lofoten Basin circulation is a separation of eddies from the main branch of Norwegian current and their westward propagation towards the central part of the basin. Because of these processes, warm and saline Atlantic waters are transported to the deeper part of the basin. Understanding the physical processes responsible for the water mass transformations in this area is of particular interest in order to apprehend the climate of the region.

For detailed study of the characteristics of mesoscale vortices we use the Ssalto/Duacs altimeter products, produced and distributed by the Copernicus Marine and Environment Monitoring Service (CMEMS) (http://www.marine.copernicus.eu) and data from the six missions of the Seagliders, covering a period from July 2012 to July 2015 (Ilker Fer and Anthony Bosse, 2017). We analyze thermohaline and dynamic characteristics of mesoscale vortices. We obtained Radial and composite structures for cyclonic and anticyclonic eddies and the orbital velocities averaged over a depth of 1000 m. To create a composite structure of cyclonic and anticyclonic eddy, hundreds of profiles of gliders intersecting vortices, which were identified by altimetry, were analyzed. For the composite structures we calculated the temperature and salinity anomalies. Altimetry-derived data on the distribution of eddy frequency, propagation speed and orbital velocity is used to quantify eddies salt, heat content and transport in the basin. 

The radius of the vortices was determined in two ways: by finding the maximum gradients of thermohaline characteristics and by the maximum rotational speed of the eddy, calculated from the glider and altimetry data (dynamic radius). The maximum speed in composite anticyclonic eddy reaches 20 cm/s. It was shown that in winter, a distinctive feature of the vertical thermohaline structure of composite anticyclonic eddy is the core of warm and saline water with a radius of 30–40 km, while the dynamic radius is 15–20 km. For the autumn season, these characteristics are much larger: 60-70 km and 30-40 km, respectively.

This work was supported by Russian Science Foundation [18-17-00027];

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Waves and vortices are detected in all rotating and stratified environments, both in the ocean and the atmosphere they contribute to weather and climate. Remote sensing is one or the best tools for monitoring the ocean surface, and due to the much larger thermal
content of the Ocean compared with that of the Atmosphere, may provide stable indicators of the Evolutionof the Earth's Climate. In particular, only recently Mesoscale Eddies (ME) and Sub Mesoscale Eddies (SME) of the order of the Rossby Deformation Radius have
revealed their high frequency and their varied generation mechanisms.
The advances in laboratory image analysis performed as SFIV techniques, may be also used at synoptic scale and using schliering type techniques, are able to map ocena surface velocity maps wth the sub measoscale eddies, some of these have a marked spiral topology.
a new research line is use fibonacci sequence scaling to explain the persistance of anticiclone features versus ciclonic ones.

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