FY 2021

Atmospheric cold pools and their influence on sea surface temperature in the Bay of Bengal

Girishkumar, M.S., J. Joseph, M.J. McPhaden, and E.P. Ram Rao

J. Geophys. Res., 126(9), e2021JC017297, doi: 10.1029/2021JC017297, View online (2021)

Recent observations show that atmospheric cold pool (ACP) events are plentiful in the Bay of Bengal (BoB) during summer (May–September) and fall (October–November) and that these events can significantly modify local air-sea interaction processes on sub-daily time scales. In this study, we examine whether the magnitude of sea surface temperature (SST) drop associated with ACP events shows any diurnal variability during summer and fall. For this purpose, we use moored buoy data with a 10-min temporal resolution at 8°, 12°, and 15°N along 90°E and a one-dimensional mixed layer (ML) model. The analysis shows a reduction in SST (ΔSST) due to ACPs in the BoB during summer and fall, with a maximum magnitude of ΔSST during the afternoon (1200–1600 LST). However, the maximum magnitude of ΔSST during the afternoon is a factor of two higher during fall (∼−0.14°C) than summer (∼−0.07°C). Analysis based on observations and ACP sensitivity experiments indicates that the shallow daytime thermocline and associated thin surface ML is the primary factor regulating the day to night difference in ΔSST associated with ACPs. The presence of this shallow daytime thermocline and thin ML amplifies the effects on SST of net surface heat loss and entrainment of cold sub-surface water associated with enhanced ACP wind speeds.

Plain Language Summary. Atmospheric cold pools (ACPs) generated from convective systems can significantly modulate air-sea interaction processes over the ocean. However, the modulation of sea surface temperature (SST) in response to intense air-sea interaction processes associated with ACPs is not yet documented in the Bay of Bengal (BoB). Our analysis based on high-temporal resolution moored buoy observations reveals a well-defined diurnal variability in the reduction of SST with an afternoon peak due to ACP activity in the BoB. One-dimensional mixed layer (ML) model sensitivity experiments suggest that the formation of the daytime thermocline and associated thin ML is the primary factor determining the enhanced reduction in SST during the afternoon compared to the night. The presence of this shallow daytime thermocline and thin ML amplifies the effects on SST of net surface heat loss and entrainment of cold sub-surface water associated with enhanced ACP wind speeds. The present study highlight that it is imperative to accurately represent ACP activity and associated air-sea interaction processes in the coupled model using for seasonal weather predictions.