The volume transport of the Somali Current during the 1995 southwest monsoon

Abstract

Abstract During the summer monsoon of 1995, two hydrographic and direct velocity sections were occupied over the continental shelf and slope off the coast of Somalia, in order to capture the flux of the western boundary current. The first section was in early June, just after the onset of the monsoon winds, when no current was observed. Instead there was an anticyclonic eddy at the boundary with a small net northward transport of 3.5±1.5 Sv . The second section was occupied in mid-September when a strong Somali Current was evident. The resulting snapshot represents the only direct velocity section of the jet structure as it flows along the western boundary. The strength of the Somali Current was 37±5 Sv . This is in general agreement with previous observations, given the temporal variability of the Current, and represents a peak value according to contemporary model simulations. The Somali Current of September extended far into shallow coastal waters of less than 200 m depth, with speeds over 150 cm s −1 , resulting in a considerable transport of 14 Sv over the shelf. Northward flow of more than 10 cm s −1 penetrated to over 2000 m depth along the continental slope, so that the subthermocline flux contributes another 13 Sv to the total volume transport. Model simulations and satellite images of sea-surface height illustrate that the Somali Current System exhibits large spatial variability on short timescales and thus differences in measured transports owe as much (maybe more) to the changing path of the Current as to variability in its strength.