The relationship of the south china sea monsoon with the south asia high and its characteristics of seasonal or interannual variations

By using NCEP/NCAR daily data of the wind, the vapour and the temperature from 1958 to 1997 as well as the monthly geopotential height and the vertical velocity data, the evolution characteristics of the potential vorticity before and after the onset of the South China Sea (SCS) monsoon are studied.An intensity index is developed by using potential vorticity.In the meantime, the relationship between the intensity index and the position as well as the intensity of the South Asia High (SAH) is analyzed.The results show that, the seasonal and interannual variations of the SCS monsoon are remarkable, the anomaly of the summer monsoon is obvious before 1978.The intensity of the SCS monsoon has a close relation with the position of the SAH. When the position of the SAH inclines to west in the previous December, the SAH will incline to north in May and the intensity of the SCS summer monsoon will much enhance.Conversely, the SAH inclines to south, then the intensity of the SCS summer monsoon will be weaker.