Seasonal Variation and Heat Preference of the South Asia High

By use of the NCEP/ NCAR reanalysis data, the seasonal variation of the South Asia high (SAH) is analyzed. The influences of temporal and spatial variations of the middle and upper level atmospheric temperatures, the visible heat sources, and the diabatic heating rates in the whole atmospheric column on the seasonal variation of the SAH are discussed. Results show that the SAH has two seasonal balancing modes, one of which is the land high in summer and the other the ocean high in winter. The land high itself can be divided into two patterns as well, that is the Tibetan high and the Iranian high. Heating fields have important impacts on the seasonal variation of the SAH. The SAH is a warm high and its center has the property of heat preference, usually locating over or moving to an area with relatively larger heating rates. The annual cycle of the SAH is mainly controlled by the seasonal process of the latent and sensible heating in South Asia. Strong shortwave radiative heating in the north at high latitudes and over the Tibetan Plateau also has an effects on the northward movement and maintenance of the SAH. The cooling effect of infrared radiation is an important cause in weakening the SAH.

IMPACTS OF SURFACE SENSIBLE HEAT FLUXES IN THE KEY AREAS OF THE TIBETAN PLATEAU ON INTERANNUAL VARIATION OF THE SCS SUMMER MONSOON INTENSITY

The impacts of the variations of surface heat fluxes over the Tibetan Plateau (TP) and surrounding areas on the interannual variation of the South China Sea (SCS) summer monsoon intensity is analyzed using the NCEP/NCAR reanalysis monthly sensible heat flux data from 1949 to 2000 and monthly mean wind and temperature field data from 1958 to 1997.The results show that there is a distinct interdecadal trend in sensible heat over the key areas of the TP and the SCS summer monsoon intensity as well as South Asia high intensity (SAHI),the transition occurs in late 1970s.The SCS summer monsoon intensity has a significant positive correlation with the variation of surface sensible heat fluxes over the northwestern part of the TP,while it has negative correlation with the surface sensible heat fluxes in the south of the TP.During the strong SCS summer monsoon year,the vertical ascending motion in the northwestern TP is strengthened,but in the southern TP it is weakened,and the position of the South Asian high is northward,while in the weak summer monsoon year,it is in the contrary.The SAHI is closely related to variation of surface heat fluxes over the TP and surrounding areas,and there exists a negative relationship between the SCS summer monsoon intensity and SAHI.