Regional climate model simulation of winter climate over Central–Southwest Asia, with emphasis on NAO and ENSO effects

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Abstract
We present a regional climate modeling study of the winter climate of Central–Southwest Asia (CSWA), focusing on the mean model climatology of temperature and precipitation, the simulated storm characteristics and the effects of El‐Nino Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) on storm activity and precipitation. Forty‐three winter seasons are simulated with the model RegCM3 driven by ERA40 reanalysis fields over a region encompassing CSWA and the Mediterranean sector. The model shows a good performance in reproducing the observed mean surface climate of the region as well as the characteristics of the western disturbances affecting CSWA. Observations show that both the NAO and ENSO have a substantial influence on the CSWA climate, particularly in the region of Northern Pakistan, Afghanistan and Tajikistan, where precipitation increases (decreases) during the positive (negative) NAO phase and warm (cold) ENSO phase. The model captures well the observed signals and a detailed storm analysis shows that they are mostly associated with an intensification of western disturbances originating in the Eastern Mediterranean and Middle East regions and moving eastward across a 500 hPa trough situated over the CSWA during the positive NAO and warm ENSO phases. The NAO and ENSO signals are reinforced by enhanced moisture sources from the Mediterranean, Caspian and Arabian Seas. Our study provides encouraging indications towards the use of the model RegCM3 for climate simulations over CSWA. Copyright © 2009 Royal Meteorological Society

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