The rainfall phenomena during the pre-monsoon period over the Indochina Peninsula in the GAME-IOP year, 1998

The rainfall phenomena in the pre-monsoon season over the Indochina Peninsula are investigated using geopotential height, wind and moisture fields by the NCEP/NCAR reanalysis, and OLR, precipitation and GPS data during the GAME-IOP year, 1998. In early and middle April, and early May, the lower OLR regions, which represent the heavy convective activity, extend southward from the mid-latitude zone to the Indochina Peninsula, bringing intermittent rainfall events in a wide region over the central part of the peninsula. The composite analysis in these three rainfall events shows that they are brought by the trough passage in the upper troposphere, which migrates eastward in the middle latitude westerlies along the southern periphery of the Tibetan Plateau. The lower tropospheric moisture inflow in these rainfall events is found to come mainly from the south and east, which shows sharp contast with the situations of inflow mainly from the west, during the non-precipitation days in the premonsoon season, and the rainfall situations after the monsoon onset in middle May.