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MMM SEMINAR NCAR

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Diurnal to Multi-day Convective Activities in the Bay of Bengal

During the Indian Summer Monsoon

Wen-wen Tung

Department of Earth and Atmospheric Sciences

Purdue University

The northern region of the Bay of Bengal is known to receive the maximum mean precipitation in south Asia during the summer monsoon. In the active phase of the monsoon, diurnal variability is a prominent mode. During the Joint Air-Sea Monsoon Interaction Experiment (JASMINE), a multi-day, vigorous, diurnally repeating, southward moving disturbances was observed in the Bay. The system initiated over land, then emanated into the Bay with a fast propagating speed of 50 km/hr (14 m/s). Satellite rainrate products from the Tropical Rainfall Measuring Mission (TRMM) suggested that similar systems might also take place during the Indian summer monsoon in 2003. Therefore, in this study, the convective activities observed over the Bay during August 2003 were numerically realized with the MM5. Two types of multi-day convective events were focused: the semi-stationary and the fast- propagating events. Both types of events were associated with well-defined circulation of the monsoon depression centered over NW Bay, were modulated by the diurnal cycle, and featured NE-SW-oriented elongated deep convective rain bands parallel to the mean flow. The rain bands were characterized by elongated ascent regions ~100 km wide accompanied by concentrated descent region, reminiscent of convectively generated gravity waves in rotational flow. The propagation of the multi-day events appeared to be the consequence of the movement of the monsoon depression driven by the large-scale circulation.

Thursday, 7 July 2005, 3:30 PM

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NCAR-Foothills Laboratory

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