The Ekman temperature and salt fluxes at 8°30′N in the Arabian Sea during the 1995 southwest monsoon

The Arabian Sea Ekman transport is an important component of the meridional overturning circulation of the Indian Ocean. Chereskin et al. (Geophys. Res. Lett. 24 (1997) 2541) presented direct estimates of the Ekman transport across latitude 8°30′N in the Arabian Sea for June and September during the 1995 southwest monsoon. In this paper, we use these measurements to determine the Ekman depth and the resultant heat and salt fluxes. In June, at the monsoon onset, the Ekman temperature and salt fluxes were estimated to be southward, 2.4 ± 0.4 PW and 0.71 ± 0.1 × 10⁹ kg s^-1. The transport-weighted Ekman temperature and salinity were 29.0 ± 0.5°C and 35.31 ± 0.03 psu, not significantly different from surface values, 29.2°C and 35.28 psu, respectively. In September at the end of the monsoon, the Ekman temperature and salt fluxes had decreased in magnitude but were still southward, 0.77 ± 0.4 PW and 0.27 ± 0.1 × 10⁹ kg s^-1. The transport-weighted temperature, 25.8 ± 0.5°C, was 1.1°C colder than the surface value, and the transport-weighted salinity, 35.83 ± 0.03 psu, was not significantly different from the surface value of 35.86 psu. For this pair of sections, the top of the pycnocline appeared to be a better approximation for the Ekman depth than either the mixed layer or a fixed depth, and our estimates of the Ekman heat and salt fluxes were integrated from the surface to the top of the pycnocline. Although uncertainty in the Ekman mass transport dominates the error in the Ekman heat and salt fluxes, determining the Ekman depth is also important in estimating the Ekman contribution to the heat budget of the tropical Indian Ocean. A decrease in Ekman temperature by 1.1°C resulted in a 5% decrease in the temperature transport estimated for September.