Circulation and water masses of the Arabian Sea

Journal of Earth System Science (Impact Factor: 0.79). 103(2):107-123. DOI: 10.1007/BF02839532

ABSTRACT The dynamics and thermodynamics of the surface layer of the Arabian Sea, north of about 10N, are dominated by the monsoon-related
annual cycle of air-sea fluxes of momentum and heat. The currents in open-sea regime of this layer can be largely accounted
for by Ekman drift and the thermal field is dominated by local heat fluxes. The geostrophic currents in open-sea subsurface
regime also show a seasonal cycle and there is some evidence that signatures of this cycle appear as deep as 1000 m. The forcing
due to Ekman suction is an important mechanism for the geostrophic currents in the central and western parts of the Sea. Recent
studies suggest that the eastern part is strongly influenced by the Rossby waves radiated by the Kelvin waves propagating
along the west coast of India.

The circulation in the coastal region off Oman is driven mainly by local winds and there is no remotely driven western boundary
current. Local wind-driving is also important to the coastal circulation off western India during the southwest monsoon but
not during the northeast monsoon when a strong (approximately 7 × 106m3/sec) current moves poleward against weak winds. This current is driven by a pressure gradient which forms along this coast
during the northeast monsoon due to either thermohaline-forcing or due to the arrival of Kelvin waves from the Bay of Bengal.

The present speculation about flow of bottom water (deeper than about 3500 m) in the Arabian Sea is that it moves northward
and upwells into the layer of North Indian Deep Water (approximately 1500–3500m). It is further speculated that the flow in
this layer consists of a poleward western boundary current and a weak equatorward flow in the interior. It is not known if
there is an annual cycle associated with the deep and the bottom water circulation.

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