A PROCESS STUDY OF THE ONSET OF THE INDIAN SUMMER MONSOON BY USING DATA INTEGRATION

The formation of the strong westerly over the Arabian Sea, which is characterized as the onset of the Indian summer monsoon provides the monsoon rainfall in India. By integrating the data sets of precipitation, outgoing long-wave radiation, cloud amount and sea surface temperature, the seasonal march of the atmospheric and earth surface conditions are examined. Based on the detail investigation of the case of 1999 and 2001, two patterns of process of the monsoon onset are identified; one associated with a cyclone event and the other with the southwest advection into the Arabian Sea but not any cyclone. For the latter cases, this paper shows that a monsoon onset is controlled by the potential temperature gradient between the Arabian Peninsula and the Arabian Sea, and between the Iran-Pakistan region and the Arabian Sea.