The Oman upwelling zone during 1993, 1994 and 1995

Satellite-derived sea-surface temperature, TOPEX/POSEIDON (T/P) sea-level a nomalies (SLAs), model wind data, and hydrographic data are used to charact erize the upwelling along the Oman coast during the US Joint Global Ocean F lux Study (US JGOFS) Arabian Sea Process Study (ASPS) in 1995 as well as to look at interannual variability in the upwelling over the period 1993-1995 . Empirical orthogonal function (EOF) analysis of the satellite-derived sea-s urface temperature (SST) at the locations of the US JGOFS standard stations shows the first mode, which represents a biannual variability, contributes 67% of the total variance. In addition, the SST shows the upwelling "front " moving offshore with the development of Southwest (SW) Monsoon in early J une 1995, reaching a maximum distance of approximately 120 km by late Augus t 1995. Finally, SST shows the persistence of cold upwelling waters for nea rly a month after the end of the SW Monsoon within the bays along the Oman coast. TOPEX/POSEIDON SLAs indicate that with the onset of the SW Monsoon, a 30-cm drop in steric height is observed along the Oman coast associated the pres ence of the cool upwelled waters. This drop in steric height sets up a hori zontal pressure gradient and results in a compensating along-shore, northea stward-flowing, geostrophic current (East Arabian Current: EAC) during the SW Monsoon. Similarly, the altimeter data slow an offshore decrease in ster ic height during the Northeast (NE) Monsoon, indicating a seasonal reversal in direction of the EAC with flow to the southwest. Subsurface temperature data indicate that the actual uplifting of isotherms associated with the u pwelling can be found to a distance of approximately 360 km from the shore and to a depth of 150-200 m. Using along-track altimetry data, we estimate that, for a region 260 km in offshore distance and 600 km alongshore, 2.2 x 10(6), 1.4 x 10(6) and 0.55 x 10(6) m(3) s(-1) were upwelled through the 1 00 m level with upwelling velocitiesO (2.0 x 10(-3)m s(-1)), during the SW Monsoons of 1993, 1994 and 1995, respectively. The reduced upwelling in the summer of 1995 is attributed to a reduction in wind-stress curl along the Arabian coast when compared to 1993 and 1993. (C) 2000 Elsevier Science Ltd . All rights reserved.