Onset of the Asian Summer Monsoon in 1979 and the Effect of the Tibetan Plateau

Abstract

Abstract The time evolution of the general circulation over Asia during an 80-day period from mid-April to early July 1979 is studied using objectively analyzed FGGE Level II-b data. Through the analyses of the wind, temperature, precipitation, outgoing longwave radiation (OLR) flux, and heat and moisture budgets in the area 0°–50°N, 40°–130°E, the major changes of the circulation leading to the onset of the summer monsoon and the role of the Tibetan Plateau in these changes are examined. During the analyzed period the general circulation underwent two distinct stages of abrupt transitions resulting in the successive onsets of early summer rains over Southeast Asia and the Indian summer monsoon. The first transition occurred in May in which low-level southwesterlies began over the longitudes east of 80°E (from the Bay of Bengal to the South China Sea), resulting in the spreading of early summer rains over Assam, the Bay of Bengal coasts of Burma and the Malay Peninsula, Thailand, Indochina and the South C...