Summer Research Fellowship Programme of India's Science Academies

A case study of the monsoon depression over the Bay of Bengal during summer monsoon 2015

Amrutha Madhusudhanan

Department of Physical Oceanography, Lakeside Campus Fine Arts Avenue Cochin CUSAT 682016

Dr. P N Vinayachandran

Professor, Centre for Atmospheric & Oceanic Sciences (CAOS), Indian Institute of Science (IISc), Bangalore 560012


The response of the Bay of Bengal (BoB) to monsoon depressions (MD) during the summer monsoon 2015 is documented in this study. In 2015, two MD formed in the BoB, one during June and the other in July. The second MD intensified into a storm. The surface variables such as temperature, winds, pressure and heat fluxes during the life-cycle of the systems are examined to understand the differential response of the upper-ocean to these disturbances. The MD of June was formed in the western Bay, while the storm in July was stationed in the head Bay. The sea surface temperature (SST) decreased on both occasions associated with the formation of a low pressure in their respective regions. The cooling in the BoB associated with these MD is more than 1.8oC and 1.5 oC respectively for the June and July systems. Similarly the sensible and latent heat flux loss is higher (>90 & 500 Wm-2) for the June MD than the July storm in the BoB. The winds are mostly southwesterly prior to the depression and strengthen as the system intensified with cyclonic circulation around the depression center. The winds are weaker at the center of the depression with higher magnitude in the southwest part of the circulation. South westerlies are restored in the region once the system weakens. Precipitation was more widespread and higher (~300 mm/day) for the July storm in the head BoB than the MD of June.

Keywords: monsoon depression (MD), sea surface temperature (SST), storm

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