The Oman upwelling zone during 1993, 1994 and 1995

Satellite-derived sea-surface temperature, TOPEX/POSEIDON (T/P) sea-level anomalies (SLAs), model wind data, and hydrographic data are used to characterize the upwelling along the Oman coast during the US Joint Global Ocean Flux 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-surface 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 June 1995, reaching a maximum distance of approximately 120 km by late August 1995. Finally, SST shows the persistence of cold upwelling waters for nearly 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 presence of the cool upwelled waters. This drop in steric height sets up a horizontal pressure gradient and results in a compensating along-shore, northeastward-flowing, geostrophic current (East Arabian Current: EAC) during the SW Monsoon. Similarly, the altimeter data slow an offshore decrease in steric 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 upwelling 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 100 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.