Convective systems in the Bay of Bengal during the Indian Summer Monsoon

Convective systems over the Bay of Bengal during August 2003 were studied with satellite and reanalysis datasets. Detailed structures of the convective organizations occurring during the entire month are further obtained through three-domain nesting (81 - 9 km) and the four dimensional data assimilation (FDDA) techniques with the MM5. In comparison with the TRMM observation, the assimilation produces reasonable rain-rate and convective activities in the Bay down to diurnal scale. It also captures a dry spell in the Bay followed by the intrusion of a convective system originated from the equatorial Indian Ocean. The diurnal and multi-day convective events in the Bay feature NE-SW-oriented elongated deep convective rain bands parallel to the mean flow, characterized by elongated ascent regions ~100 km wide accompanied by concentrated descent region. The assimilated convective systems in the Bay, however, lack the definite southward-propagating tendency found in the observation. Case studies utilizing cloud system-resolving simulations are in progress in the hope to examine the propagation mechanism.