DETERMINATION OF ONSET DATE OF THE SOUTH CHINA SEA SUMMER MONSOON IN 2006 USING LARGE-SCALE CIRCULATIONS

Since the South China Sea (SCS) summer monsoon (SCSSM) is pronouncedly featured by abruptly intensified southwesterly and obviously increased precipitation over the SCS, the lower-tropospheric winds and/or convection intensities are widely used to determine the SCSSM onset. The methods can be used successfully in most of the years but not in 2006. Due to the intrusion of Typhoon Chanchu (0601) that year, the usual method of determining SCSSM onset date by utilizing the SCS regional indices is less capable of pinpointing the real onset date. In order to solve the problem, larger-scale situations have to be taken into account. Zonal and meridional circulations would be better to determine the break-out date of SCSSM in 2006. The result indicates that its onset date is May 16. Moreover, similar onset dates for other years can be obtained using various methods, implying that large-scale zonal and meridional circulations can be used as an alternative method for determining the SCSSM onset date.