Distribution of cloudiness and categorization of rainfall types based on INSAT IR brightness temperatures over Indian subcontinent and adjoining oceanic region during south west monsoon season

To understand the relationship between rain intensity and brightness temperature, Cloud Top Brightness Temperature (CTBT) derived from INSAT three hourly IR radiances having a resolution of 0.25 × 0.25 deg. is compared with corresponding TRMM PR Rain Rate (TPRR) for the Indian Summer Monsoon periods of 2007 and 2008. BT value ranges corresponding to events of various intensities of rain in the four major raining sub regions identified in Indian subcontinent and surrounding ocean are compared. The sub regions identified are (1) Head Bay of Bengal, (2) Central Indian land region, (3) Eastern Arabians Sea and West coast of India and (4) South West Indian Ocean. BT values are grouped into classes of 10°K bin width between 270 and 180°K. Number of occurrence of three classes of rain (light - >4.5 mm, moderate - 4.5-9 mm and heavy 9.0 mm and above cumulative for 3 h) belonging in each BT classes is calculated. It is observed that the three classes of rainfall have distinct characteristic BT ranges. This rain category - BT range relation has geographical (spatial) variability. This could be due to the variation in types of clouds prevalent in the sub regions considered. The present study improves the understanding of the structure and spatial variability of cloudiness and rainfall in and around Indian region during monsoon season.