The Southwest Monsoon Current east of Sri Lanka
P. N. Vinayachandran*1, Yukio Masumoto*1,2, and Toshio Yamagata*1,2
*1 Instititue for Global Change Research, Frontier Research System for Global Change
*2 Department of Earth and Planetary Physics, University of Tokyo, Japan
The general eastward flow in the north Indian Ocean during summer, which is called the Southwest Monsoon Current (SMC), flows eastward south of India, turns around Sri Lanka and enters the Bay of Bengal. The intrusion of the SMC into the Bay of Bengal is studied using the XBT observations along the shipping route between Sri Lanka and Malaca Strait, TOPEX / POSEIDON sea surface height anomalies, and an ocean general circulation model.
The intrusion appears first as a broad northward shallow (confined to the upper 200m) flow in the central part of the Bay of Bengal during May. As the season advances it moves westward, intensifies and becomes narrow. The mean seasonal (May-September) transport of the SMC into the Bay of Bengal is about 10Sv. The zonal variation of the geostrophic velocity across 6N calculated using the XBT data compares well with that from TOPEX / POSEIDON altimeter data. However the SMC in the XBT data is faster (40cm/s) than in the altimeter data or the numerical simulation (25cm/s). Harmonic analysis of the depth of 20C isotherm together with a simple forced Rossby wave model demonstrates that the SMC east of Sri Lanka is forced by both Ekman pumping in the Bay of Bengal and Rossby wave radiation associated with the spring Wyrtki jet in the equatorial Indian Ocean.
