CHARACTERISTICS OF ATMOSPHERIC HEAT SOURCE ASSOCIATED WITH THE SUMMER MONSOON ONSET OVER THE SOUTH CHINA SEA AND THE POSSIBLE MECHANISM RESPONSIBLE FOR LATE OR EARLY ONSET OF THE MONSOON

Characteristics of atmospheric heat source associated with the summer monsoon onset in the South China Sea (SCS) are studied using ECMWF reanalysis data from 1979 to 1993. A criterion of the SCS summer monsoon onset is defined by the atmospheric heat source. Applying this criterion to the 15-year (1979～1993) mean field, the onset of the SCS summer monsoon occured in the fourth pentad of May. And this criterion can also give reasonable results for the onset time of the SCS summer monsoon on a year to year basis. In addition, pretty high correlation has been found between the onset time of the SCS summer monsoon and the zonnal mean vertically integrated heat source Q1t 40 S in April. The causes for the late or early onset of the SCS summer monsoon and the close relationship between the onset time and the zonnal mean vertically integrated heat source Q1t 40 S in April might be explained by the variations in intensity of the Hadley circulation.