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. •The relationship between brightness temperature derived from INSAT IR radiances and rain intensity from TRMM PR over Indian Monsoon region is analyzed.•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

Kerala floods in consecutive years - Its association with mesoscale cloudburst and structural changes in monsoon clouds over the west coast of India

Kerala, located at the southwest tip of India, witnessed disastrous floods during the monsoon seasons of two consecutive years, 2018 and 2019. This paper provides a detailed analysis of these two flood events using data from multiple sources. The unusually unstable and convective nature of the 2019 event, as detectable in its higher cloud tops and evidently fuelled by anomalously warm local sea temperatures, raises concerns regarding the changing patterns of rainfall over the southern parts of the west coast of India. Specifically, our analysis reveals that the flood of 2019 in Kerala satisfies the criteria for a mesoscale cloudburst (MsCB) event, more common in the north but a very rare and never before reported phenomenon in the Kerala region. Rainfall exceeding 50 mm in 2 h has been reported from many places between 8.00 and 22.00 UTC on the August 8, 2019. Satellite-derived rainfall and cloud microphysical parameters further reveal the uniqueness of the 2019 MsCB event. If 2019 is a harbinger of how global warming may continue to affect this region, transformations of the cloud structure and the recurrence and character of intense rainfall events could pose a major threat to the highly vulnerable Western Ghats ecosystems