Mechanisms of diurnal variation and its year-to-year variation of tropical precipitation using numerical model

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In order to check the ability of the regional climate model, one month time integration was performed. The results of this simulation showed that the migration of large scale precipitation systems accompanied by the eastward movement of MJO was represented in the model, the representation of rough patterns of precipitation systems was robust, and the absolute values of precipitation amount significantly differ among results using different cumulus parameterization schemes.In order to study the mechanism of the diurnal variation of precipitation, numerical simulations of the diurnal variation of precipitation in Bangladesh was performed, where the maximum precipitation occurs in the midnight to the early morning. It was revealed that the precipitation was not triggered by the convergence between the southeasterly monsoon and cold katabatic wind from the Megalaya mountain in the night but the monsoon wind was lifted by the Megalaya mountain directly or by the cold pool formed by the precipitation system in the previous day. We also studied the mechanism of the 10-20 days variation of precipitation using observed data.In the aspect of development of global climate models, we performed ensemble simulations to study the effects of soil wetness and soil temperature on the atmospheric circulations. It was concluded that soil conditions controlled the surface evaporation only in regions with relatively dry surface relative humidity. Therefore, it was suggested that the predictability of the atmospheric circulation over the such dry regions would increase provided the soil condition determined by, for example, remote sensing techniques.