Mesoscale processes in the northern Arabian Sea: Linking in situ observations to remote-sensing

The PHYSINDIEN 2019 campaign occurred in the Northwestern Arabian Sea, during the spring intermonsoon, between 16 and 25 °N. Along its 3000 km transect, it sampled 5 anticyclones, 3 cyclones and 2 cyclonic submesoscale coherent vortices (SCV) with continuous hydrological and velocity measurements. Remarkably, the two cyclonic SCV were located beneath surface mesoscale anticyclones. Also, a water mass analysis shows that small anticyclones with Persian Gulf Water (PGW) are found in the Gulf of Oman, while anticyclones further south are shallower vortices containing Arabian Sea High Salinity Water (ASHSW). Comparison of in situ data with the META atlas, a state-of-the-art eddy detection and tracking atlas based on altimetry, reveals that eddy radii are often underestimated by remote sensing. In this atlas, eddy tracks are often discontinuous due to missing detections. Both hydrological measurements and remote-sensing tracking are however consistent in indicating that along the southern Omani coast anticyclones are formed offshore during the spring intermonsoon, near the center of the Arabian Sea. These results underline the diversity of surface and subsurface eddies in the sparsely explored Arabian Sea, and provide insight on the potential bias of their remote detections.