Simulation of the Indian Summer Monsoon and its Variability using the JMA Global Model

Abstract

   Ten-year integrations of the JMA global model at T106 and T42 horizontal resolutions were compared to examine the role of model resolution in simulating the Indian monsoon and its variability. It has been found that both T106 and T42 models simulate mean monsoon climatology reasonably well in terms of the large-scale monsoon flow. The T106 model simulates rainfall distribution in western and northwestern parts of India better than the T42 model.
   Correlation of interannual variability (IAV) of simulated rainfall with observed IAV is poor. The simulated IAVs of the Indian monsoon rainfall for both models do not have a strong correlation with the SST, either. The T42 model simulated the rainfall variability for 1987/88 better than the T106 model. Monsoon rainfall variability may be largely due to internal dynamics in both models. Internally generated variability may be larger in T106 model than T42 model simulations.
   Rainfall anomaly patterns obtained from T42 model simulations are better than those of T106 model simulations for the two pairs of good and bad monsoon events (1988/87 and 1983/82). Responses of both the coarser and finer resolution models to the same imposed surface forcing differ over the Indian monsoon region.
   Both models simulate the synoptic evolution of the monsoon quite well. Monsoon activity in the T106 model is more intense than in the T42 model. Rainfall distribution is better obtained from T106 model simulations than T42 model simulations. This suggests that further work is necessary in relating intraseasonal variations with interannual monsoon variability for understanding the nature of monsoon variability.