Diurnal variability of atmospheric cold pool events and associated air-sea interactions in the Bay of Bengal during the
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Diurnal variability of atmospheric cold pool events and associated air‑sea interactions in the Bay of Bengal during the summer monsoon Jofia Joseph1,3 · M. S. Girishkumar1 · M. J. McPhaden2 · E. Pattabhi Rama Rao1 Received: 17 May 2020 / Accepted: 15 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Atmospheric cold pools generated from convective downdrafts can significantly modulate air-sea interaction processes, though the variability in cold pool events is not yet documented in the Bay of Bengal (BoB). In this study, the seasonal and diurnal variability of cold pool events (defined as a drop in air temperature greater than 1 °C within 30 min) in the BoB is examined using moored buoy measurements with 10-min temporal resolution at 8°N, 12°N, and 15°N along 90°E. The analysis shows that cold pools are plentiful and frequent during summer (May–September) and fall (October–November) compared to winter (December-February) and spring (March–April). Results also indicate a significant diurnal variability at 15°N and 12°N (but not at 8°N) during summer, with more frequent and intense cold pool events in the afternoon. Cold pools lead to an intensification of turbulent heat exchange between the ocean and atmosphere, with increased latent heat loss (~ 80 Wm−2) through both an increase in wind speed and reduction in air specific humidity and increased sensible heat loss (~ 40 Wm−2) due primarily to air temperature drops. There is also a significant diurnal variability in these air-sea exchanges during the summer, with a twofold enhancement in latent and sensible heat fluxes associated with afternoon vs nighttime cold pools events. Finally, we establish the connection between the enhancement of afternoon cold pool events and southeastward propagating synoptic-scale rainfall activity on diurnal time scales from the western BoB.
1 Introduction To improve coupled model simulations of Indian Summer Monsoon rainfall, it is important to document and understand the variability that occurs at the ocean and atmosphere interface. Air-sea interaction processes vary across a wide range of space scales and temporally from diurnal to interannual and longer time scales in the tropics (Bhat et al. 2001; Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00382-020-05506-w) contains supplementary material, which is available to authorized users. * M. S. Girishkumar [email protected] 1
Ministry of Earth Sciences (MoES), Indian National Centre for Ocean Information Services (INCOIS), Hyderabad 500 090, Telangana, India
2
Pacific Marine Environmental Laboratory (PMEL), National Oceanic and Atmospheric Administration (NOAA), Seattle, WA 98115, USA
3
School of Ocean Science and Technology, Kerala University of Fisheries and Ocean Studies, Panangad, Cochin 682506, India
Webster et al. 2002; Sengupta et al. 2001; Bernie et al. 2005, Bernie et al. 2007; Seo et al. 2007; 2014; Rao and Sivakumar 2000; Shenoi and Shankar 2002, Shenoi et al. 2009; Pra
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