C-SWOT 2023 blog: C-SWOT – WEMSWOT companion campaigns at the mid-term point

By Pierre Garreau and Franck Dumas

Last week-end, after ten days of companion navigation, the R/V L’Atalante and the R/V Tethys II met in Mahon (Minorca) for a joint port call. These two experiments at sea are part of a wider observation strategy concomitant with the fast-sampling phase of SWOT satellite. They are focused on an area characterized by small mesoscale structure (O(40km)) in a weak internal wave environment more prone to exhibit clear mesoscale signal.

This 2023 spring is marked in the north western Mediterranean basin by numerous anticyclones eddies and filaments that arise from both side of the basin (at the edge of the northern current, see Fig 1) and to the north of the Balearic front). An opportunity for the SHOM and IFREMER teams to share their experience and give a first glance to the data acquired under the swaths of the SWOT satellite running from the island of Menorca to Toulon. This meeting happened during the on-going SWOT deployment which has come to the end of its commissioning phase to switch to the fast-sampling one. This year, the North Western Mediterranean basin is home to numerous eddies and filaments that the two research vessels have sampled together for several days. An impressive amount of data has been collected and will be processed and compared to the satellite equivalent observations.

Vertical hydrological and hydrodynamical sections along and across SWOT swaths were performed with hull-mounted ADCPs and a towed undulating vehicle (the Seasoar on R/V L’Atalante) or a winch-controlled profiler (the MVP-200 on R/V Tethys II) providing currents, salinity, and temperature down to 300m deep.  SVP and Carthe drifters were launched in observed velocity gradients and dedicated drifters recorded sea states under the swaths. These different methods of collecting surface currents should make it possible to distinguish geostrophically balanced currents from inertial, internal or wind-induced currents.

Hoping for an equally successful second leg of the C-SWOT campaign, we look forward to compare the in-situ data to SWOT observations by next September.

Fig 1: R/V L’Atalante arriving at the wharf of Mahon where stand the R/V Tethys II.
Fig 2 : Chlorophyl a fields from Olci sensor onboard Sentinel III satellite.
Fig 4: Cross-basin section (bottom left) of temperature (top left), salinity (top right) and their relationship plotted on a T-S diagram (bottom right).
Fig 5: Sampling tracks of the first phase of the twin C-SWOT/WEMSWOT experiments.
Fig 6: CARTHE buoy being deployed from R/V Tethys II’s deck by Margot Demol.
Fig 2 : Chlorophyl a fields from Olci sensor onboard Sentinel III satellite.
Fig 7: Sunset from portside passageway of R/V Tethys II.
Fig 8: Moonlight above C-SWOT’s mission leader.
Fig 9: Trèfle buoy preparation.
Fig 10: MedArgo float ready to be deployed.
Fig 11: Glider deployment.
Fig 12: The R/V Tethys II off La Ciotat, Côte d’Azur, Southern France.
Fig 13: Transhipment of Tethys II’s crew onboard L’Atalante.
Fig 14: VMP 500 for microstructures observations in the hands of Jean-Baptiste.
Fig 15: Towed undulating vehicle to perform vertical hydrological sections within SWOT’s swaths.