Impact of Indian Ocean sea-surface temperature anomaly on Indian summer monsoon precipitation using a regional climate model

The present study uses a recent version (Version-III) of National Center for Atmospheric Research (NCAR) Regional Climate Model (RegCM3) to simulate the Indian summer monsoon rainfall (ISMR). Since RegCM3 is used for the first time for such a study over south Asia, its performance was tested for different conditions of ISMR. The RegCM3 is integrated at 60 km horizontal resolution from April I to October I for three contrasting rain years corresponding to drought (2002), normal (2001) and excess (1994). The monsoon circulation features simulated by the RegCM3 are compared with those of the National Center for Environmental Prediction (NCEP)/NCAR reanalysis, and simulated precipitation is validated against observations from the Global Precipitation Climatology Centre (GPCC) data sets. Validation of the wind patterns at lower and upper levels shows that the RegCM3 simulated results are close to the NCEP/NCAR reanalysis. Similarly, the patterns of precipitation distribution simulated by the RegCM3 are close to the GPCC (except over the west coast). Features of intra-seasonal oscillation during different rain years are also examined by applying a frequency filter and the technique of wavelet analysis to rainfall data. Results indicate that a faster (10-20 days) mode dominated during an excess rain year and a slower (30-60 days) mode during a deficient rain year, which agree well with the observations (GPCC). The influence of increase in sea-surface temperature (SST) by 0.6 degrees C on the following summer monsoon circulation and rainfall over India has also been studied. The SST (warm) experiments show that the regional warming of SST over the Indian Ocean enhanced the monsoon precipitation mainly over south peninsular India, west peninsular India and the Indian Ocean and reduced precipitation over northeast India. Copyright (C) 2007 Royal Meteorological Society.