Comparative assessment of the roles of diabatic processes in the Indian Monsoon System

Global climate models produce diverse simulations of many aspects of monsoon circulation and precipitation. Notably, significant biases remain in CMIP5 simulations of the progression of the wet and dry seasons and precipitation variability in the Indian summer monsoon region. A novel method is used to examine the individual roles of different diabatic heating processes in the onset, break, poleward extent and withdrawal of the monsoon precipitation over India. The methodology, which has been applied to CMIP5 models and global reanalyses, exploits the relationship between diabatic heating of different nature such as latent heating, radiative cooling and sensible heating from heat low, and the corresponding profiles of wind divergence to quantify the relative contributions of circulations associated with each type of forcing to the moisture budgets of the monsoon system. By comparing the results from analysis of CMIP5 and global reanalyses, processes that are responsible for biases and inter-model spread in the CMIP5 simulations of Indian monsoon precipitation are identified. A significant portion of these biases and spread in mean monsoon season precipitation among CMIP5 models are found to be related to the differences in divergence profile in precipitation regions which partially determines the effectiveness of the latent heat release in forcing moisture convergence.