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The seasonal prediction of the Indian summer monsoon rainfall (ISMR) is very important for India, especially for planning strategies towards management of agricultural production and water resources. The seasonal prediction of the monsoon by dynamical models is based on the fact that the slowly varying boundary conditions like sea surface temperature (SST), soil moisture, snow cover etc. exert significant influence on atmospheric development on seasonal time-scales in the tropics. Although the seasonal mean monsoon seems to be potentially predictable, atmospheric GCM simulations have not shown enough skill in capturing the inter-annual variations in the monsoon rainfall. Indian Summer Monsoon has limited potential predictability. It has also been recognized that ocean-atmosphere coupling is crucial in determining the potential predictability of the monsoon. Therefore, a coupled ocean-atmosphere climate model is required for predicting the monsoon. It is essential to develop and improve a system of fully coupled ocean-atmosphere-land modelling system for dynamical prediction of the seasonal mean monsoon rainfall. IITM is developing such a system and it will be transferred to the India Meteorological Department (IMD). This model is useful for giving lot of spin-off in science, e.g., one should be able to study the role of air-sea interactions on monsoon variability and predictability in more details.
Recent studies have demonstrated the possibility of achieving improved skills in simulating the seasonal mean monsoon rainfall by using ocean-atmosphere coupled models. This improvement appears to result from more accurate representation of the coupled interactions between the Indian monsoon and the tropical oceans. During 11th and 12th Five Year Plan periods, IITM scientists have setup an ocean-atmosphere coupled model on its IBM P6 575 (Prithvi) & Aaditya High Performance Computing (HPC) system and made long period free runs as well as hindcast (retrospective) experiments to test the model with set of initial conditions (e.g., with ensembles of atmospheric and oceanic initial conditions). The model outputs have been analyzed and its performance for simulating Indian Summer Monsoon Rainfall(ISMR) was examined. Certain biases in model simulations have been identified and efforts are being made to reduce these model biases. In addition to the research efforts on the coupled model, IITM has provided, for the first time in India, reliable experimental coupled dynamical monsoon prediction to IMD for further dissemination to general public. Certain modifications (e.g., better physical parameterizations and better representation of air-sea interaction processes, higher resolution) has been incorporated for making this model better suitable for our region, leading to enhanced model skill of simulating ISMR. At present the model using for seasonal prediction (CFSv2) at a horizontal resolution of 38km for atmosphere is the one of the highest resolution in the world and is able to achieve a better skill for ISMR. The model is set up under “monsoon mission” program of Ministry of Earth sciences and is handed over to IMD for operational use by 2017. In the succeeding phase of monsoon mission, the group is working further on model development and use these model improvements for developing application for sectors like agriculture, hydrology, wind energy forecasts etc which has crucial role in the life and economy of the people.