Regional distribution of deep clouds and cloud top altitudes over the Indian subcontinent and the surrounding oceans

Abstract

The Bay of Bengal (BoB) and the east equatorial Indian Ocean are among the most intense deep convective regions over the tropics. Long‐term monthly mean distributions of deep clouds and the regional differences in the cloud top brightness temperature (CTBT) over the Indian subcontinent and the surrounding oceanic regions (the northern and eastern BoB, the southeast Arabian Sea, and the eastern equatorial Indian Ocean) are derived using National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer data for a period of 10 years and are compared with the direct observations of cloud top altitude (CTA) using Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). The deepest clouds are found to occur over the northern BoB (NBoB) during the June–August period. The most probable CTBT in this region is ∼12 K lower than that over the other deep convective regions. CALIPSO observations also show that the frequency of occurrence of CTA peaks at an altitude of ∼16.5 km over the NBoB, which is ∼1 km higher than that over the other regions. Strong convergence of horizontal wind between the surface and ∼200 hpa level and large divergence above, combined with the most favorable sea surface temperature (>28°C), might be mainly responsible for the highest CTA being observed over the NBoB. The annual variation of the base altitude and thickness of the tropical tropopause layer (TTL) and the upper tropospheric temperature are closely associated with the corresponding variations in the deep cloud fraction. Considerable fraction of deep clouds occurs within the TTL over the BoB during the June–August period.