The Characteristics of Spatial and Temporal Distributions of Convective Rainfall and Stratiform Rainfall in the Asian Monsoon Region and their Possible Mechanisms

Based on the Tropical Rainfall Measuring Mission (TRMM) data in the latest twelve years, the characteristics of spatial and temporal distributions of convective rainfall and stratiform rainfall in the Asian monsoon region are analyzed. The results show that: on the multi-year mean timescale, the spatial distributions of convective rainfall and stratiform rainfall in the Asian monsoon region show the characteristics of meridional variation, such as, the stratiform rainfall dominating over the subtropical monsoon regions to the north of 25°N, whose percentiles are above 50% and increase with latitudes, however, the convective rainfall dominating over the regions to the south of 25°N, whose percentiles are about 55% and show homogeneous spatial distribution characterstics. The spatial distributions of convective and stratiform rainfall pixels percentiles show that the stratiform cloud is the main rain cloud all over the Asian monsoon region (the area mean of stratiform rainfall pixels percentiles is above 60%). On the seasonal timescale, the convective rainfall and stratiform rainfall show distinguished seasonal variation (their standard deviations are above 10%) over the northern part of the East Asian monsoon region (to the north of 25°N) which is called the subtropical monsoon region. The stratiform rainfall dominates over this region, whose percentiles are about 85% in winter, but the percentiles of the stratiform (convective) rainfall decrease (increase) gradually and reach the minimum 55% (maximum 45%) with the coming of summer and the northward shift of monsoon rainband. With the advance of time, the percentiles of the stratiform (convective) rainfall increase (decrease) gradually to the winter status. However, the convective rainfall and stratiform rainfall show little seasonal variation (their standard deviations are below 3%) over the South Asian monsoon region and the southern part of the East Asian monsoon region (to the south of 25°N) which is called the tropical monsoon region. The convective rainfall dominates over this region, whose percentiles are from 50% to 65% all the year round. The analyses of dynamic factors and thermodynamic factors show that the spatial and temporal distributions of the convective rainfall and the stratiform rainfall in the Asian monsoon region are controlled by the vertical wind shear dynamic factor of the monsoon circulation. However, the thermodynamic factors, such as temperature, moisture, equivalent potential temperature, and convective available potential energy, influence the intensity, extension, and duration of the convective rainfall and the stratiform rainfall. These dynamic factors and thermodynamic factors seem to have their critical values.