Influence of the south-north bias of the South Asia High on the water vapor distribution in the upper troposphere-lower stratosphere of the Asian monsoon region

Abstract

Based on the ERA-40 reanalysis data provided by the European Interim Numerical Forecast Centre from 1958 to 2002, the influence of the north-south bias of the South Asia High(SAH) on the water vapor distribution in the upper troposphere-lower stratosphere of the Asian monsoon region is analysed. It is shown that: (1) The north-south bias of SAH has little influence on the position of the 200 hPa water vapor high value centre, which mainly affects its intensity; and it has a great influence on the position and intensity of the 100 hPa water vapor high value centre; It has little effect on the water vapor distribution at 70 hPa. (2) In the south years of SAH, the anti-cyclone is abnormally weak, the vertical ascending motion is relatively insubstantial, and the water vapor transported to the upper troposphere is less than the north years. Therefore, the water vapor high value in the south years is smaller than that in the north years. (3) Abnormal temperature distribution of 200 hPa in anticyclone is consistent with the abnormal distribution of water vapor, and the warm centre is conducive to the formation of high water vapor. It is shown that the distribution of water vapor in the anticyclone range is caused by the interaction of temperature field and circulation field. This study has a certain reference meaning for understanding the stratospheric-tropospheric exchange of the Asian monsoon region.