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

Abstract

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.

Eddy‐Induced Temperature and Salinity Variability in the Arabian Sea

“…Upwelled waters are then recirculated by large-scale circulation and mesoscale features. Climatological summer SLA (Figure 1a) clearly reveals strong quasi-permanent eddies like the Great Whirl around 52°E and 9°N and the Socotra Eddy to its northeast (Akuetevi et al, 2016;Beal & Donohue, 2013;Trott et al, 2018;Figure 1a,b). Additionally, the SSS field reveals low salinity values within the Great Whirl with the Arabian Sea high salinity water mass about its exterior (Beal & Donohue, 2013; Figure 1c).…”

Eddy Tracking in the Northwestern Indian Ocean During Southwest Monsoon Regimes

“…For eddies having maximum amplitudes above 40 cm, CEs along the Somali Current region tend to propagate in a clockwise trajectory as they displace about the larger-radius AEs (Jensen, 1991;Matsuura & Yamagata, 1982). Akuetevi et al (2016) describes this phenomenon of an asymmetric dipole where smaller cyclonic eddies generated by cyclonic vorticity bursts characteristic of a low-latitude western boundary current circle about their larger-radius counterparts (AEs). During the 22-year period of study, more CE trajectories (seven) than AE trajectories (two) were observed with maximum amplitudes greater than 40 cm (Figures 4j and 4k respectively, 10-20, 20-30, 30-40, and > 40 cm).…”

Influence of Mesoscale Features on Mixed Layer Dynamics in the Arabian Sea

“…Large anticyclonic eddies like the Great Whirl and Socotra Eddy have been known to advect smaller cyclonic dipoles whose low SSHs are sourced from upwelled waters along the Somali Coast and Arabian Peninsula (Akuetevi et al, ; Beal & Donohue, ). For this reason, large anticyclonic eddies in this region have been observed to coalesce (Akuetevi et al, ; Schott et al, ), which explains the decreasing number of anticyclonic eddies following the second week of July (Figure a) while maintaining overall larger radii and smaller amplitudes (which are so strong in cyclonic eddies along upwelling zones). Trott et al () found a higher number of large anticyclonic eddies (with amplitudes greater than 20 cm) in the Arabian Sea during stronger monsoon seasons.…”