Analysis of the Monsoon Response to Radiative Perturbations in GCM Simulations

Abstract

It has been long known, at least since the pioneering work of Halley and Hadley,that the primary cause of monsoon circulation is to be found in the differential heating between ocean and land surfaces (Webster, 1986). Numerous studies have attempted to unravel the interactions between the physical and dynamical processes that play a part in the genesis of monsoons (for a detailed historical account of the earlier attempts see Kutzbach ,1986). The monsoon appears as a very complex phenomenon which has a direct impact on the economy of some of the most populated regions of the world (Das, 1986). Therefore a prediction of monsoons could be of great economic interest. However, though some statistical methods have shown promising results, a deeper understanding of the dynamics and physics of the monsoon is a prerequisite for further improvements of the forecasts. General Circulation Models (GCMs) can play an essential part in the experimental study of climate dynamics, and indeed have been applied to the problem of monsoon simulation for more than 20 years (Washington and Daggupaty, 1975; Hahn and Manabe, 1975; Gilchrist, 1977). Since these early studies, a large number of numerical simulations of the monsoon have been performed and reported in the literature (the more recent ones are Zwiers, 1993; Meehl, 1994; 1993; Zhang, 1994). A significant part of monsoon variability is due to the influence of various anomalous surface forcings, which can modify the thermal contrast between land and ocean (Shukla, 1986).