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Ocean Surface Topography from Space
Merging of satellite and in situ observations for the analysis of meso and submesoscale dynamics


Alexis Chaigneau - (LEGOS)

  Yves Morel
  Rosemary Morrow

  Hervé Demarcq
Francesco D'Ovidio
Dudley Chelton
Ronan Fablet
  Thierry Delcroix
Florence Birol
Patrice Klein
Xavier Carton


Merging of satellite and in situ observations for the analysis of meso and submesoscale dynamics
A schematic representation of the main goals of each WP.

WP1: Eddy vertical structure from the merging of altimetry and Argo float data (left panel, vertical temperature anomalies in mesoscale eddies, from Chaigneau et al. [2011]) and their impact on the submesoscale dynamics (right panel, mean distribution of Lyapunov exponents inside mesoscale eddies).

WP2: Identification of the nature (surface or subsurface) of mesoscale eddies from satellite observations only, merging altimetry and SST data. Each of the idealized eddies would correspond to particular SLA and SLA/SST ratios.

WP3: Improvement of large-scale tracer SST and SSS fields and fronts by stirring and advecting these fields using altimetric-derived velocities.

Our proposal aims to improve our knowledge of the meso and submesoscale dynamics by merging altimetric data with various other satellite datasets (sea-surface temperature (SST) and salinity (SSS)) and/or in-situ observations. Three original techniques have been identified and are proposed in the present project:
  • The three-dimensional (3D) structure of mesoscale eddies and their role in structuring the submesoscale dynamics and associated mixing.
  • The development and test of a method to identify subsurface-intensified structures from satellite observations only (altimetry and SST).
  • The improvement of the resolution of ocean fronts by combining large-scale tracer fields (SST, SSS) with lateral stirring computed from altimetric currents

These technique are based on specific methodologies, are independent and their development will constitute the three Work Packages (WPs) of the project. However, the combination of the different approaches will be studied too, with an aim to reconstruct the precise structure of oceanic eddies and understand the observed evolution.

Concerning the mesoscale dynamics, we will investigate the 3D structure of mesoscale eddies merging information from multi-sensor satellite data (altimetry and SST), and in-situ profiles acquired by Argo profiling floats. To this task, two different approaches will be used and combined: (i) in the WP1, we will apply an observational method that allows reconstructing the mean vertical thermohaline properties of mesoscale eddies in the region under study, combining multi-mission satellite altimetry products and Argo hydrographic profiles [Chaigneau et al., 2011]; (ii) in the WP2, a new method will investigate the possibilities of using satellite altimetry and sea-surface temperature data only, to reconstruct the three-dimensional variations of the mesoscale dynamics. In particular, the comparison of surface circulations computed from geostrophy (from altimetry data) and surface quasi-geostrophy (from SST observations) theories will allow determining the signature of subsurface intensified structures. This open question is fundamental for anticipating future satellite altimetry missions such as SWOT that will acquire sea-surface height data having similar resolution as SST observations.

In terms of submesoscale dynamics, the WP1 will investigate the interaction between the mesoscale eddies detected by altimetry and (i) the submesoscale dynamical filaments and associated mixing determined from altimetry maps and Lagrangian advection diagnostics [e.g. d'Ovidio et al., 2004]; (ii) the SST fronts automatically detected from MODIS images using a novel identification scheme [Nieto et al., 2012]. The WP3 will be devoted to improve large-scale tracer SST and SSS fields, obtained from interpolated Argo in-situ data, by stirring and advecting these fields using altimetric-derived velocities. This method will also be used to improve the resolution of fronts in SSS fields observed from SMOS data. The WP3 will finally focus on the improvement of the resolution of the gridded altimetric geostrophic velocities used for the Lagrangian advection which in turn will help to improve the frontal structures in the upper ocean fields.

The proposed project will be performed preferentially in the North-East Atlantic and the Indian Ocean. These regions encompass a relatively high-number of available Argo floats needed for WP1-3, and enhanced-resolution altimetric products, that will be used in WP3, were recently developed in these regions. This project will also focus in the NW Mediterranean Sea where airborne tests of the AirSWOT instrument will be carried out and new regional high resolution altimetric data set should be developed for this experiment (see TOSCA AirSWOT proposal). Although the techniques and methods developed in the frame of this project will be applied in these 3 contrasted regions, if robust and relevant, they will be easily applicable for other domains of interest.

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