The life cycle of submesoscale eddies generated by topographic interactions

Type Article
Date 2019-11
Language English
Author(s) Morvan Mathieu1, L'Hégaret Pierre1, Carton Xavier1, Gula Jonathan1, Vic Clement2, Sokolovskiy Mikhail3, Koshel Konstantin4
Affiliation(s) 1 : LOPS, Univ. Brest-CNRS-IFREMER-IRD, IUEM, France
2 : National Oceanographic Center, University of Southampton, European Way, Southampton, SO14 3ZH, UK
3 : Institute of Water Problems of the RAS, Ul Gubkina 3, Moscow, 199333, Russia, Shirshov Institute of Oceanology of RAS, 36 Nahimovskiy pr., Moscow, 117997, Russia
4 : V.I.Il’ichev Pacific Oceanological Institute, 43, Baltiyskaya Street, Vladivostok, 690041, Russia
Source Ocean Science (1812-0784) (Copernicus GmbH), 2019-11 , Vol. 15 , N. 6 , P. 1531-1543
DOI 10.5194/os-2019-3
WOS© Times Cited 10

The Persian Gulf Water and Red Sea Water are salty and dense waters recirculating at subsurface in the Gulf of Oman and the Gulf of Aden respectively, under the influence of mesoscale eddies which dominate the surface flow in both semi-enclosed basins. In situ measurements combined with altimetry indicate that the Persian Gulf Water is driven by mesoscale eddies in the form of filaments and submesoscale structures. In this paper, we study the formation and the life cycle of intense submesoscale vortices and their impact on the spread of Persian Gulf Water and Red Sea Water. We use a three-dimensional hydrostatic model with submesoscale-resolving resolution to study the evolution of submesoscale vortices. Our configuration is an idealized version of the Gulf of Oman and Aden: a zonal row of mesoscale vortices interacting with north and south topographic slopes. Intense submesoscale vortices are generated in the simulations along the continental slopes due to two different mechanisms. The first mechanism is due to frictional generation of vorticity in the bottom boundary layer, which detaches from the topography, forms an unstable vorticity filament, and undergoes horizontal shear instability that leads to the formation of submesoscale coherent vortices. The second mechanism is inviscid and implies arrested topographic Rossby waves breaking and forming submesoscale coherent vortices where a mesoscale anticyclone interacts with the topographic slope. Submesoscale vortices subsequently drift away, merge and form larger vortices. They can also pair with opposite signed vortices and travel across the domain. They can weaken or disappear via several mechanisms, in particular fusion into the larger eddies or erosion on the topography. Particle patches are advected and sheared by vortices and are entrained into filaments. Their size first grows as the square root of time, a signature of the merging processes, then it increases linearly with time, corresponding to their ballistic advection by submesoscale eddies. On the contrary, witout intense submesoscale eddies, particles are mainly advected by mesoscale eddies; this implies a weaker dispersion of particles than in the previous case. This shows the important role of submesoscale eddies in spreading Persian Gulf Water and Red Sea Water.

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