TripleA -- PML's planned use of altimetry in the Arctic, Atlantic and Agulhas regions

Graham Quartly (Plymouth Marine Laboratory, United Kingdom)


Andrey Kurekin (PML, United Kingdom); Ben Loveday (EUMETSAT, Germany); Peter Miller (PML, United Kingdom); Francesco Nencioli (CLS, France)

Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)

Session: Salient results from the 2017-2020 OSTST PIs

Presentation type: Type Forum

This presentation is a very succinct summary of the activities carried out by Plymouth Marine Laboratory that were related to their OSTST 2017-2020 proposal.

1. In the Arctic, we completed work with CLS on developping an altimetry processor for Envisat data in the Arctic. This encompassed validation of waveform classifications using simultaneous optical data from MERIS, design of an "adaptive" retracker able to cope with returns from ocean, sea-ice and leads, and application of the necessary environmental corrections. This work was complemented by involvement in a meeting at ISSI (International Space Science Institute) bringing together altimetrists interested in oceanography and sea-ice, and culminating in a lengthy review paper.

2. In the Atlantic, we studied the westward progression of a pair of Agulhas eddies that merged at the Mid Atlantic Ridge and then continued onward to the Brazil coast. By using Argo profiles that occurred close to the features we were able to determine volume and density anomalies as they progressed on their two and a half year journey. This showed that although volume was roughly constant there was interchange with their surroundings. A numerical experiment seeding the surface velocity field with virtual drifters every 6 months confirmed that after crossing the Walvis Ridge there was modest dissipation along the route, but that the majority of the tracked particles escaped upon reaching the Brazil coast.

3. In the Agulhas, we explored the potential for using features in SST and ocean colour to give reliable current directions, with these frontal orientations being combined with across-track altimetry currents to provide vector fields. The assessment was carried out across the East Madagascar Current as it flows around the south of the island. In this region it often has strong thermal and ocean colour contrasts, and we had had three moorings deployed for 14 months along a Jason-1 track. Good agreement was found between in situ measurements and inferred along-track velocities provided that the features were within 60 degrees of the normal to the track.

4. In the global component, we looked at the differences between sigma0 and SWH estimates from the SAR retracker on Sentinel-3A and the values obtained via PLRM processing. Whilst that work is still ongoing, early results showed that the wave height estimates from the SAR processing read high (relative to PLRM) by an amount that increased with wave height, whereas a climatology based on the PLRM data was relatively unbiased with respect to Jason-3 for the same period. This suggests that revisions are needed to the SAR retracking algorithm.

Graham Quartly
Plymouth Marine Laboratory
United Kingdom