A Diagnostic and Modeling study on South Asian Summer Monsoon Onset

The main focus here is to understand the Asian Summer Monsoon onset processes. The process is of 70-day duration starting from 15 pentads before the monsoon onset over Kerala, when a large convective heat source forms over north Indian Ocean and adjoining West Pacific, which generates a fully developed cross equatorial Low Level Jet stream. During this process there is formation of a warm pool over the Bay of Bengal first followed by a warm pool over the Arabian Sea and active air-sea interaction. We then developed a method for an objective determination of the date of monsoon onset over Kerala for operational use. Using this method we have objectively derived the onset dates for each year of the period 1960 to 2003. The simulation of the positive feedback process between the convection and low-level wind field associated with the summer monsoon Onset is tried next using an atmospheric General Circulation Model. We also devised methods for predicting the date of monsoon onset more than a week ahead.