The sea surface circulation pattern over the coast of Peninsula Malaysia's Eastern Continental Shelf during Northeast Monsoon (December-February) and Southwest Monsoon (June-August) are derived using the seasonally averaged sea level anomaly (SLA) data from altimetric data and 1992-2002 Mean Dynamic Ocean Topography. This altimetric data has been derived from multi-mission satellite altimeter TOPEX, ERS-1, ERS-2, JASON-1, and ENVISAT for the period of nineteen years (1993 to 2011) using the Radar Altimeter Database System (RADS). The estimated sea level anomaly (SLA) have shown similarity in the pattern of sea level variations observed by four tide gauges. Overall, the sea surface circulations during the NE and SW monsoons shows opposite patterns, northward and southward respectively. During the SW monsoon, an anti-cyclonic circulation has been detected around the Terengganu coastal area centred at (about 5.5 o N 103.5 o E) and nearly consistent with previous studies using numerical modelling. The estimated geostrophic current field from the altimeter is consistent with the trajectory of Argos-tracked Drifting Buoys provided by the Marine Environmental Data Services (MEDS) in Canada.
High resolution mean surface velocity field of the Arabian Sea was derived by combining sea level anomalies based on satellite altimetry data with the surface drifter data. The mean current field exhibits the western boundary Somali Current, weak westward North Equatorial Current, weak West Indian Coastal Current. Besides strong currents, the Arabian Sea exhibits strong mesoscale eddy activity in the western side. The seasonal surface circulation changes of the Arabian Sea and variability associated with the Indian Ocean Dipole (IOD) events were determined. The Somali Current is northward during summer, with a speed above 1.8 m/s in July and it reverses towards south in winter. Significant changes were found in the flow pattern during IOD events. An anticyclonic gyre near the equator was a conspicuous feature during the positive IOD. Further, the Great Whirl shows an earlier formation and dissipation during the positive IOD. Notably, a delay of southward reversal of the Somali Current is found during the positive IOD. The southward flow of West Indian Coastal Current during summer monsoon is much stronger during the positive IOD and the northward flow in fall is prominent during negative IOD. The eastward Equatorial Jet is absent in fall and instead an opposite (westward) flow prevails during the positive IOD. Enhanced Chl-a concentration occurs during the negative IOD, compared to the positive IOD, especially in the western Arabian Sea. The wind-driven upwelling and mesoscale eddies are significantly modifying the Chl-a distribution along the Somali Coast.
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