Impact of Tropical Cyclones On The Ocean Heat Budget In The Bay of Bengal During 1999: 2. Processes and Interpretations

Abstract

The impacts of two consecutive, strong tropical cyclones (TCs) from October–November in 1999 on the Bay of Bengal (BoB) heat budget are examined using the Hybrid Coordinate Ocean Model. The model uses atmospheric conditions from reanalysis, reconstructed TC winds, and satellite-observed winds and precipitation. We conduct a series of diagnostic experiments to isolate the model’s response to the individual TC-associated forcings. During the TCs, the BoB ocean heat content (OHC) is reduced, primarily due to TC-wind induced southward ocean heat transport (OHT) and a reduction in surface downward radiation due to increased cloudiness. BoB OHC is largely restored in the following months via enhanced surface heat fluxes, associated with cold wake restoration, and positive northward OHT. The TCs’ downward heat pumping effect is estimated to be ~
1.74  10^18 J near the end of February 2000, which is less than estimates using previously published methods based on surface observations. The relatively weak heat pumping results from freshwater input by intense monsoon rainfall and river discharge in the BoB, which stabilizes stratification, forms a barrier layer, and generates temperature inversions during seasonal surface cooling. As a result, early stage TC winds entrain the warm barrier layer water and enhance enthalpy loss in the southeastern Bay, while mature stage TC winds erode the barrier layer, decrease SST through upwelling and entrainment of deeper cold water and reduce enthalpy loss in the northwestern Bay. Our findings suggest TC winds may significantly alter the interseasonal BoB heat budget through OHT and surface heat fluxes.