Articles | Volume 12, issue 1
Research article
01 Feb 2016
Research article |  | 01 Feb 2016

Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study

C. Q. C. Akuetevi, B. Barnier, J. Verron, J.-M. Molines, and A. Lecointre

Abstract. Three hindcast simulations of the global ocean circulation differing by resolution (1/4 or 1/12°) or parametrization or atmospheric forcing are used to describe the interactions between the large anticyclonic eddies generated by the Somali Current system during the Southwest Monsoon. The present investigation of the Somalian coherent eddy structures allows us to identify the origin and the subsequent development of the cyclones flanked upon the Great Whirl (GW) previously identified by Beal and Donohue (2013) in satellite observations and to establish that similar cyclones are also flanked upon the Southern Gyre (SG). These cyclones are identified as potential actors in mixing water masses within the large eddies and offshore the coast of Somalia.

All three simulations bring to light that during the period when the Southwest Monsoon is well established, the SG moves northward along the Somali coast and encounters the GW. The interaction between the SG and the GW is a collision without merging, in a way that has not been described in observations up to now. During the collision the GW is pushed to the east of Socotra Island, sheds several smaller patches of anticyclonic vorticity, and often reforms into the Socotra Eddy, thus proposing a formation mechanism for that eddy. During this process the GW gives up its place to the SG. This process is robust throughout the three simulations.

Short summary
The NW Indian Ocean is the siege of two very intense anticyclonic eddies, the Great Whirl and the Southern Gyre, the rapid development of which makes their observation difficult. Model simulations propose an interaction scenario between the two eddies not described in observations up to now. When the summer monsoon intensifies, the Southern Gyre moves northward, collides with the Great Whirl and takes it place. The Great Whirl is pushed to the east of Socotra Island and forms the Socotra Eddy.