CLIMATIC FEATURES OF SCS SUMMER MONSOON ONSET AND ITS POSSIBLE MECHANISM

The high quality dataset from the SCS (South China Sea) Monsoon Experiment and 40-year NCEP/NCAR reanalysis data are used to investigate the large-scale features and abrupt change in meteorological elements during the onset of the SCS summer monsoon.It is found that the SCS summer monsoon establishment is characterized by the South Asian high migrating swiftly from the eastern side of Philippines to the northern part of Indo-China Peninsula and the enhancement of the Bay of Bengal trough and equatorial westerly over the Indian Ocean associated with the equatorial westerly expanding towards northeastward,and followed by the mid-low latitude interaction and continuous retreat eastward of the western Pacific subtropical high.Further study shows that the meridional temperature difference and the zonal wind vertical shear over the Asian lower latitudes also experience abrupt change during the onset of the SCS summer monsoon. Numerical experiments reveal that the Indian Peninsula acts as a critical role for the enhancement of the Bay of Bengal trough with a cyclonic difference circulation excited to the east side of the peninsula through ground sensible heating in such a way that the SCS summer monsoon occurs prior to the Indian summer monsoon.