Why were cool SST anomalies absent in the Bay of Bengal during the 1997 Indian Ocean Dipole Event?

Abstract

The most important center of atmospheric convection associated with the Indian summer monsoon is located in the Bay of Bengal. This tendency was enhanced during the 1997 Indian Ocean Dipole (IOD) event and cool SST anomalies due to upwelling in the east were restricted to the south of about 5°N in the bay. However, sea surface height anomalies associated with the upwelling propagated all the way to the north bay. Using XBT data collected in the bay, and a high resolution ocean general circulation model simulation, we propose that the permanent, low-salinity, highly stratified, near-surface pool in the bay prevented the IOD-related upwelling from influencing the SST. The strong near-surface stratification in the bay cannot be broken down by the observed winds there, therefore it ensures that internal ocean dynamics cannot have an impact on SST. As a result, atmospheric convection over the bay may be decoupled from ocean dynamics.