Simulation of Indian summer monsoon: sensitivity to cumulus parameterization in a GCM

Abstract

AbstractHindcasts for the Indian summer monsoons (ISMs) of 2002 and 2003 have been produced from a series of numerical simulations performed with a general circulation model using different cumulus parameterization schemes. Ten sets of ensemble simulations have been produced without using any vegetation scheme but by prescribing the monthly observed SST from the ECMWF (European Centre for Medium Range Weather Forecasts) analyses. For each ensemble, ten simulations have been realised with different initial conditions that are also prepared from the ECMWF data: five each from the April and May analyses of both the years. Stream function, velocity potential with divergent winds at 200 hPa, winds at 850 hPa and rainfall patterns with their anomalies have been analysed and interpreted. The large‐scale upper and lower level circulation features are simulated satisfactorily. The spatial structure of predicted July monsoon rainfall over India shows a fair agreement with the GPCP (observed) pentad rainfall distribution. The variability associated with all‐India June–July simulated rainfall time series matches reasonably well with the observations in 2003, but the model fails to simulate the observed variability in July 2002. Further evaluation of the model‐produced precipitation in seasonal simulations is done with the help of empirical orthogonal functions (EOFs) of the GPCP rainfall over India. Since the first four EOFs explain a significant part of the total variance of the observed rainfall, the simulated precipitation is projected on to these modes. Thus, the differences in simulated and observed rainfall fields manifest in the time series of their expansion coefficients, which are utilised for inter‐comparison/evaluation of model simulations. Copyright © 2006 Royal Meteorological Society