Atmospheric Cold Pools in the Bay of Bengal

Abstract

Abstract Atmospheric cold pools, generated by evaporative downdrafts from precipitating clouds, are ubiquitous in the Bay of Bengal. We use data from three moorings near 18°N to characterize a total of 465 cold pools. The cold pools are all dry, with a typical temperature drop of 2°C (max. 5°C) and specific humidity drop of 1 g/kg (max. 6 g/kg). Most cold pools last 1.5-3.5 hours (max. 14 hours). Cold pools occur almost every day in the North Bay from April to November, principally in the late morning, associated with intense precipitation that accounts for 80% of total rain. They increase the latent heat flux to the atmosphere by about 32 W/m2(median), although the instantaneous enhancement of latent heat flux for individual cold pools reaches 150 W/m2 . During the rainiest month (July), the cold pools occur 21% of the time and contribute nearly 14% to the mean evaporation. A composite analysis of all cold pools shows that the temperature and specific humidity anomalies are responsible for ~90% of the enhancement of sensible and latent heat flux, while variations in wind speed are responsible for the remainder. Depending on their gust front speed, the estimated height of the cold pools primarily ranges from 850 to 3200 m, with taller fronts more likely to occur during the summer monsoon season (Jun-Sep). Our results indicate that the realistic representation of cold pools in climate models is likely to be important for improved simulation of air-sea fluxes and monsoon rainfall.