Simulation of Inter-annual Variability of Summer Monsoon Rainfall in a GCM over India and Nepal

Abstract

Monsoon is one of the major phenomena over the entire tropical belt that is associated with the regional climate primarily through rainfall. The importance of the monsoon rainfall is prolonged to a large fraction of the world’s population and the socio-economic prospect of the region. Community Atmosphere Model (CAM) (v4, 0.47°×0.63°) developed by NCAR has been used for this study. Two experiments have been conducted; viz. CLIMO Exp. using climatological SST and OBSST Exp. using observed monthly OI-SST.The climatology of surface temperature, wind circulation and rainfall over the extended Indian monsoon (60°E–110°E;0°N–40°N) region has been generated through 30-year long-term simulation of CAM and analyzed using different observed Climatology viz. TRMM rainfall, NCEP reanalysis, IPCC, UD generated climatology, IMD & DHM in-situ observations etc. The model derived monthly averaged surface temperature climatology over the study region has a good correlation with the observed IPCC and NCEP climatology. Both the simulations are able to capture the sea surface temperature over the Indian Ocean and over the landmass. The model simulation shows heat sink region over the northwestern part of India and spreads over the eastern part almost reaching Bay of Bengal region and gets slowly reduced after approaching the southwest monsoon rains. The seasonal temperature variation over the study region, monthly mean, maximum and minimum are comparable. The climatological wind circulation at 850 hPa and 200 hPa are well simulated. The reversal of wind during pre-monsoon and monsoon season over the region are well simulated by both the experiments. Therefore, this study using high resolution modeled data provides an insight of the model credibility in capturing the climatic variability over the region (India, Nepal and its surroundings) and its capability for predicting the inter-annual variation and projecting the climate of the globe. The present study aims to measure the skill of the state-of-art AGCM in simulation of ISM rainfall and investigate the inter-annual variation using the climatological and observed SST.