Equatorial Indian Ocean Sea surface slope changes (Wyrtki Jet extent) using altimeter data
Kalyani Chikka(1) and Ali MM(2)
Woman scientist,Belur Campus, Wind Tunnel Road,
Bangalore 560 037,
(2) Natioanl Remote Senisng Agency, Head, NRSA, Balanagar, hyderabad-500 037, India
Equatoiral Indian ocean (EIO) behaves uniquely compared to the other oceans because of the monsoonal wind features prevailing over this region. The current direction also chnages because of the wind reversal. Since the coriolos force vanishes near the equator the surfacial water is pushed downwind in the wave guide via Yoshida Jet/Kelvin wave. This jet is sometimes referred as the "WYRTKI JET". The presence of the Sumatra coast and the adjoining islands piles up the water there at the east (Wyrtki, 1973). This results change in the zonal slope of the mixed layer (O'Brien and Hulbert 1974, Ali 1993 etc). Studying the extent of this type of jet in the open ocean over a better temporal and spatial scales is practically impossible with conventional measurements from buoys/ships. The advent of satellite altimetry thus gave an oppurtunity for such a study.
In this study we have analysed 14 years of the altimeter data (1990-2004) over the Equatorial Indian Ocean (EIO) (10 deg S-10deg N, latitude and 50-95E longitude) to study the latitudinal extent and the interannaul variations of the Equatorial Jet. To study the propagation of the jet, monthly mean sea surface elevations have been constructed using sea surface height (derived from altimeters) for different latitudinal belts spanning the EIO. Two latitudinal belts have been considered for this study. One ranges from 1deg S-1deg N to 10deg S to 10 deg N in total having 10 belts with varying latitudinal extents. The other ranges from 10deg S-9deg S to 9deg N-10deg N, with 20 latitudinal belts each with 1deg extent.
Monthly sea surface slopes along 50-95deg E for the 30 latitudinal belts have been obtained for the entire altimeter period by fitting a linear regression between the sea surface elevation and longitude.
The jet propagation has been studied in detail during various seasons using 14 years of the altimeter sea surface height .