Onset and Evolution of the 1998 East Asian Summer Monsoon

During the May-June 1998 South China Sea Monsoon Experiment (SCSMEX), a sounding network was established in the South China Sea (SCS) and surrounding region to investigate the onset and development of the East Asian monsoon. This network was contained within the larger domain of the GEWEX Asian Monsoon Experiment (GAME). The raw sounding observations have been subjected to quality-control procedures and gridded over a large region from 10S to 40N and from India to the western Pacific.

Using the gridded fields, the evolution of the mean flow during the onset of the monsoon is documented. Analyses of temperature, moisture, zonal and meridional components of the wind, divergence and vertical motion over the longitudes of the SCS reveal the northward advance of the monsoon. This northward advance will be contrasted with that over the Indian subcontinent. Also documented are changes in the strength and properties of the boundary layer and tradewind cumulus layer during the period of onset. Special soundings over the SCS have enabled these changes to be determined in a detail heretofore not possible.