Abstract:

Using the data collected during 2010~2012 Eastern Indian Ocean (EIO) cruises, we analyzed the hydrographical features in the upper layer of the southern Bay of Bengal (BoB) and eastern equatorial Indian Ocean (EEIO) during spring monsoon transition. We also studied the variations of meridional geostrophic transport and the thermocline at the mouth of the BoB. The results show that the equatorial westerly wind bursts become the dominant force in this region during spring intermonsoon transition around March-May. They change the equatorial pressure gradient force from eastward to westward by transporting the Arabian Sea water to the east, and weaken the equatorial undercurrent. At the BoB mouth, the wave propagation in the equator enhances the northward water volume transport, mixes the water masses form the Arabian Sea and BoB, and increase the salinity gradient. In addition, the remote forcing of equatorial waves leads to the formation of a cyclonic eddy at the BoB mouth. The remote forcing also deepens the thermocline at the west end in the southern BoB, while the upper-layer low salinity water keeps it shallow at the east end even though the thermocline in the EEIO is deepened.

Key words: Eastern Indian Ocean, monsoon transition, hydrography, geostrophic current, thermocline