TN-59 : Regional GCM for the monsoon area

Abstract

Monsoons, which affect the largest land masses, have been the subject of study on every scale from simple local studies to circulation simulation on giant computers (the so-called fifth and sixth generation computer systems like CYBER-205 and CRAY series) in recent years. An extensive work has been carried out on different physical aspects of monsoon viz., onset and withdrawal of monsoon, regional energetic, heat and moisture budgets, synoptic components etc. Indian monsoon, which is associated with abundant seasonal precipitation (mainly rains) has particularly attracted the attention of the world meteorological community leading to a number of extensive studies.

Precipitation, an important climatic element for hydrological processes has been simulated by various general circulation models. The global general circulation on one hand and the hydrologic cycle on the other are the nature's mechanism to maintain balance of water and temperature on earth. During the last two decades, many investigators have coupled the hydrologic processes (land surface) models and the atmospheric general circulation models (GCM). There are, however, gaps in the hydrological parameterization for the interlinking of atmospheric land surface processes. Sensitivity tests on general circulation models have revealed that the fluctuations in sea surface temperature, soil albedo, ground hydrology and snow cover are likely to influence the intensity of monsoon rains. These need to be validated using surface and sub-surface data.

This note gives a review of the existing monsoon circulation models with special emphasis on the regional aspects. Different physical processes which affect Indian monsoon are also dealt with. The sensitivity of the monsoon circulation model outflow to surface albedo, soil moisture and evapotranspiration, snow cover, sea surface temperature has been discussed. The need of the quantitative forecast of precipitation for use in the forecasting of runoff is emphasized.