Seasonal variation of cross‐equatorial flow in the Somali Current

Abstract

Moored current measurements in the Somali Current on the equator of approximately 1‐year duration reveal a seasonal cycle of the vertical current structure which is substantially different during part of the year from that previously perceived from measurements in the boundary current away from the equator. In particular, during the winter monsoon the southwestward flow at the surface reaches down only to little more than 100 m, while a northward countercurrent exists below down to 400 m. Observed current structure is quite well reproduced by a numerical model with high vertical and reasonable horizontal resolutions. Overall conclusions are that the equatorial and off‐equatorial circulation of the Somali Current are separate systems during most of the year and that remote forcing from the east along the equator appears to be a minor effect in the seasonal variability of near‐surface flow in the equatorial Somali Current.

The Life Cycle of Annual Waves in the Indian Ocean as Identified by Seamless Diagnosis of the Energy Flux

“…The results also illustrate how a large-scale monsoon leads to the formation of the Somali jet. In boreal winter along the African coasts ( Figure S2a), the southward signals of the SC originate from the North Monsoon Current while the northward signals of the EACC originate from the South Equatorial Current [SM01; Schott, 1986;Nagura & Masumoto, 2015]. These equatorward boundary currents meet each other around the equator to turn eastward as the South Equatorial Counter Current (Düing & Schott, 1978;Swallow et al, 1991), in such a way as to relax negative geopotential anomaly in the western equatorial region ( Figure S2b).…”

Intensification of upwelling along Oman coast in a warming scenario

“…The Somali current has a pronounced seasonal variability in tune with the seasonal reversal of the south Asian monsoonal winds. The current reverses its direction from southward to northward as the season changes from winter to summer [ Schott and McCreary , ; Schott , ]. During summer monsoon season (i.e., from June to September), a reversal to this boundary current from northward to southward below 700 m depth is also observed [ Schott , ; Leetmaa et al , ].…”

“…During summer monsoon season (i.e., from June to September), a reversal to this boundary current from northward to southward below 700 m depth is also observed [ Schott , ; Leetmaa et al , ]. The SC north of 5°N is usually considered as a separate northern branch as the cross‐equatorial flow turns offshore between equator and 5°N [ Schott , ]. However, during the late phase of summer monsoon (August–September) the flow is continuous, composing a single current system [ Shankar et al , ; Schott , ].…”

“…The current reverses its direction from southward to northward as the season changes from winter to summer [Schott and McCreary, 2001;Schott, 1986]. During summer monsoon season (i.e., from June to September), a reversal to this boundary current from northward to southward below 700 m depth is also observed [Schott, 1986;Leetmaa et al, 1982]. The SC north of 5 ∘ N is usually considered as a separate northern branch as the cross-equatorial flow turns offshore between equator and 5 ∘ N [Schott, 1986].…”

“…One of the prominent features at the coast of Somalia during summer monsoon is the development of a strong anticyclonic gyre called "Great Whirl" (GW) [Beal and Donohue, 2013;Schott and McCreary, 2001;Leetmaa et al, 1982;Bruce, 1968]. Within the anticyclonic gyre the water converges and downwells [Song et al, 2004] while intense upwelling and advection of upwelled waters are seen along the northern flank of the GW.…”