1. Mesoscale/sub-mesoscale dynamics and SWOT
P.Y. Le Traon, P. Klein, B. Chapron,
J. Isern (Ifremer), G. Dibarboure (CLS)
Outline
Capabilities of conventional altimetry
Interpretation of altimeter wavenumber spectra
SWOT potential contributions 1

2. Summary of Jason-1/ENVISAT (T/P-ERS-1/2) mapping capabilities
(based on formal mapping error analysis and simulations with Los Alamos North Atlantic model) (Le Traon an Dibarboure, 1999; Le Traon et al., 2001, 2002)
Jason-1/ENVISAT : Sea level can be mapped with an accuracy of 5 to 10% of the signal variance*. Velocity mapping error from 20 to 40% of the signal variance.
3 or 4 altimeters needed to reduce errors by a factor of 3
(needed for surface currents)
*corresponds to periods < 20 days and/or wavelengths < 200 km (see next figures and discussion on the role of high frequency signal in Le Traon and Dibarboure, 2002)

3. Resolution of Jason+ENVISAT maps
(wavelengths >200 km)
Sea level spectra from along-track and mapped data
Only wavelengths larger than 200 km are reproduced on mapped data
Ducet et al., 2000

4. Altimeter wavenumber spectral slopes in the mesoscale band very closely follow a k-11/3 slope as predicted by surface quasi-geostrophic theory (SQG) (Le Traon et al;, 2008; Lapeyre and Klein, 2006; Klein et al., 2007)
SQG could thus be a much better dynamical framework than the QG turbulence theory to describe the ocean surface dynamics.
These results point out the important dynamical role of small scale structures. They also offer new perspectives for the analysis and interpretation of satellite data.
In particular, the joint use of SST, OC and altimetry should allow a much better description of the 3D ocean state (including vertical velocity) (Isern et al. , 2006)
k-11/3
Le Traon, Klein, Hua and Dibarboure, JPO, 2008 4

5. High resolution altimetry (SWOT) mesoscale/submesoscale investigations
Should allow a characterization of submesoscale signals. Scales (wavelengths/2) between 10 and 100 km.
Noise is a major issue (a goal of 1 cm / 1 km for an uncorrelated noise is quite challenging !).
Time sampling will remain an issue for some applications.
Conventional altimeter noise level (2.5 cm – 7 km)
10-20 km
SWOT noise level ? (1 cm / 1 km)
Ducet et al., 2000

6. Proposed Ifremer / CLS investigations for SWOT preparation
Analysis of sampling capabilities of SWOT using very high resolution basin scale models (1 -2 km) (SSH, velocity and vorticity). Analysis of SWOT measurement errors (white/correlated noise, roll errors) and their impact on mission objectives. Use tools developed and tested for conventional multiple altimeter and WSOA studies (Le Traon et al. 2001, Le Traon and Dibarboure, 2002).
Science investigations on mesoscale/submesoscale dynamics. Use very high resolution model to characterize mesoscale/submesoscale signals and the potential contribution of SWOT.
Analyze the synergy of high resolution altimetry with SST, OC and SAR data in the framework of SQG dynamics. Use of SSH, SST and OC to reconstruct 3 D ocean circulation (incl. Vorticity and vertical velocity) (Isern et al., 2006, 2008). Impact for ocean forecasting. 6