Simulation of characteristic features of Asian summer monsoon using a regional climate model

Abstract

The paper presents the results of simulation experiments aimed at predicting the characteristic features of Asian Summer Monsoon during the middle of the century (2041-60) resulting from global climate change. The modelt used is 1-IacERM2 regional climate model of the Hadley Centre for Climate Prediction and Research, UK. Two simulation experiments of 20 years length have been performed for the Asian domain, namely, one with a fixed amount of greenhouse gas concentration corresponding to 1990 levels called the 'control' (CTL) experiment and the other with the annual compound increase of l % in the greenhouse gas concentration for 2041-60 from 1990 onwards called the 'greenhouse gas' (GHG) experiment. The annual compound increment of 1 %. in the greenhouse gas concentration has been adopted from the projection given by the intergovernmental Panel for Climate Change (IPCC). The experiments have brought out some of the changes in the characteristic features of mid-century Asian summer monsoons that are expected to occur due to increased anthropogenic emissions. The most significant change seems to be a general northward shift of the monsoon trough (MT) in the lower troposphere (850 hPa) throughout the monsoon season over the Indian region. The simulation results have shown an increase of about 1-2 hPa in the sea level pressure (SLP) over the Arabian Sea during the monsoon resulting in an anomalous anticyclone over there in the lower troposphere. This would mean the weakening of Low Level Jet (1..1-1) and the Arabian sea branch of the monsoon current The model has simulated a decrease in the frequency of the monsoonal cyclonic disturbances over the north Indian Ocean under the warmer sea surface conditions which conforms to the observed decreasing trends in the frequency of monsoon depressions in recent decades. The experiments have shown that the Heat Low over Pakistan and adjoining northwest India, may intensify and shift slightly eastward during the monsoon. The model has simulated the strengthening of Tropical Easterly Jet (TEJ) at 100 hPa {the location of TEI core ) over the southern parts of Indian sea between 5° - 10° R, especially during the first half of the monsoon season.