Prof. Xavier Carton

Prof. Xavier Carton

LOPS/IUEM/UBO

Rue Dumont d'Urville

Email: xcarton@univ-brest.fr

Research interests: vortex dynamics, study of outflows from marginal seas, slope current dynamics

The 3D structure of mesoscale eddies in the northeastern Arabian Sea and their impact on submesoscale dynamics

Abstract

In the Northeastern Arabian Sea, the pathway of the salty Persian Gulf Water outflowing from the Persian Gulf is strongly impacted by the mesoscale and submesoscale features which evolve in the Sea of Oman and around the Arabian Peninsula. We use ARGO floats colocalized with eddies detected in the Arabian Sea for the period 2000-2015 from altimetric data, to extract anomalies of temperature and salinity related to mesoscale eddies. It allowed us to compute a composite 3D structure of mesoscale eddies in the region. These structures are validated with in situ observations and are shown to be representative of the typical mesoscale activity of the Sea of Oman.

Using a primitive equation simulation at high resolution, we show that the composite cyclonic eddy is unstable. A mixed barotropic/baroclinic instability causes the eddy to destabilize. This leads to the deformation of the core of the eddy, and the formation of spiral arms around it. The azimuthal mode 2 dominates, and the growth of the perturbation is roughly constant, reflecting the linear stage of the instability. The spiral arms then become unstable because of a shear instability in the surface layer. This forms a crown of long-standing submesoscale coherent vortices around the eddy. Also, the edge of the eddy undergoes an intense frontogenesis leading to the occurring of imbalanced circulation and generation of negative Ertel Potential Vorticity. The core of the eddy is then eroded by a symmetric instability which propagates inward.