Performance of RegCM4 for Dynamically Downscaling of El Nino/La Nina Events During Southwest Monsoon Over India and Its Regions.

This study presents the interannual variation in the summer monsoon rainfall during the El Nino Southern Oscillation (ENSO) phases, that is, El Nino and La Nina throughout the Indian subcontinent and its subregions during 1986–2010. The analysis includes the performance assessments of the regional climate model (RegCM4) in simulating Indian summer monsoon rainfall through comparison with India Meteorological Department rainfall data. Observation clearly demonstrates that the El Nino/La Nina produced weaker/strong monsoon rainfall over India and it increases the interannual variability of the southwest monsoon. The capability and skill of RegCM4's Grell and Mix99 cumulus parameterization scheme in simulating Indian summer monsoon rainfall associated with extreme climate are usually higher in "dry" conditions rather below average for the accurate simulation of "wet" conditions. Also, model performance was good in defining the characteristics, spatial distribution, and trend of a dry spell during ENSO phases with observation. The model‐simulated spatial and temporal value of wet spell during ENSO produces overestimated value over all India. Plain Language Summary: This study has been performed with the motivation of understanding the southwest monsoon drought/flood characteristics associated with El Nino and La Nina events. Climate change variability studies are of utmost importance for the planning of agriculture and economic policy. With this motivation, an attempt has been made to study the distinguishing features of Indian summer monsoon rainfall during El Nino and La Nina years over the Indian subcontinents and its subregions with Regional Climate Model (RegCM4). The finding of our study highlights the capability and skill of RegCM4's Grell cumulus parameterization scheme in simulating Indian summer monsoon associated with extreme climate are usually higher in "dry" condition rather below average for the accurate simulation of "wet" condition. The index of maximum count of consecutive dry days and consecutive wet days helps in accessing the deficient/excess rainfall over a regionalized and localized area. Key Points: The modulation of spatial and temporal south west monsoon rainfall during ENSO phases are prominentEl Nino and La Nina episodes control the probability of occurrences and length of wet spell and dry spell during monsoonThe skill of RegCM4 in simulating ISMR during the extreme ENSO phases are better in "dry" conditions rather below average for the accurate simulation of "wet" conditions [ABSTRACT FROM AUTHOR]