Inter-annual variability of sea surface temperature, wind speed and sea surface height anomaly over the tropical Indian Ocean

Abstract

Being land-locked at the north, the Indian Ocean and its surrounding atmosphere behave in such a way that the ocean-atmosphere interaction over this domain is different from that over the other oceans, exhibiting a peculiar dynamics. The sparse data coverage over the Indian Ocean was one of the several reasons for the incomplete information accumulated to date. With the advent of satellite technology and advanced modeling techniques the availability of data with space and time became easier. Here we have made an attempt to study the annual and inter-annual variability of certain prominent processes occurring over the tropical Indian Ocean. The monthly mean values of Wind Speed (FSU), Sea Surface Temperature (REYNOLDS) and Sea Surface Height Anomaly (TOPEX/POSEIDON) over a period of 5 years from 1993 are used for this investigation. The first EOF mode of seasonal and non-seasonal data set gives annual and inter-annual variability over the tropics. A strong signal of dipole is observed in all the fields during 1994 and 1997 coinciding with the El Nino events. The reversal of westerlies at the equator appeared to be responsible for the formation of anomalous cooling and warming near Sumatra and Somali, respectively. The oscillation of westerlies from south to the equator and back and its association with the pre- and post-monsoon Equatorial Jet is evident over 62 degrees E and 90 degrees E. The amplitude of this oscillation is more at the eastern section. A propagation of high sea surface is noticed at both 62 degrees E and 90 degrees E from the equator to 25 degrees S, which seems to be associated with the above meridional oscillation of the westerly wind. The time-longitude section at the north (10 degrees -15 degrees N) and south (10 degrees -15 degrees S) exhibits the propagation of Rossby waves.