Precipitation Structure and Convective Intensity Over South-East South Asia During Active and Break Spells of the Indian Summer Monsoon Using TRMM, GPM, Megha-Tropiques Satellites and Reanalysis Data

Abstract

In this study, we investigated the precipitation structure (PS) and convective intensity (CI) of precipitation features (PFs) using the multiple sensors onboard on TRMM and GPM for active and break spells (ACT and BRK-Ss) during Indian summer monsoon seasons (1999-2021). Microwave-based observations showed that during ACT-Ss, a higher frequency of PFs is observed over the Himalayan Foothills and northern western Ghats (WGs). Eastern Himalaya Foothills (EHFs), southern India, the Indian Equatorial Ocean, and the Arabian Sea (AS) have a higher frequency of PFs during BRK-Ss. The major differences in PS during ACT and BRK-Ss are observed over WGs and southern-western Himalayan Foothills (S-WHFs). Infrared-based measurements showed that the Bay of Bengal (BOB) and S-WHFs have the deepest Cumulonimbus clouds (minimum brightness temperature) during both ACT and BRK-Ss, but the numbers over BOB are twice as high compared with S-WHFs. S-WHFs have the strongest CI (40 dBZ radar reflectivity has the highest altitude) and precipitation tops (20 dBZ radar reflectivity has the highest altitude) during ACT-Ss. WGs and the Indo-Gangetic Plain (IGP) consist of intense and larger PFs during the BRK-Ss. PFs with the highest horizontal extension, and, which are contributing to higher surface rainfall observed over north-central India and BOB during ACT Ss, but during BRK-Ss, they shifted to EHFs and the Burma-Myanmar coast. Lightning activity is higher at S-WHFs and EHFs during ACT-Ss but shifted at the eastern longitudes of EHFs and southern India during BRK-Ss. Relative humidity (RH) profiles are used to investigate the moist and dry atmospheric conditions during ACT and BRK-Ss. Megha-Tropiques-based sounders showed a higher fraction of RH vertical profiles above mid-troposphere (above 500 hPa) over BOB and S-WHFs during ACT-Ss. WGs and IGP have a higher fraction of RH vertical profiles above the mid-troposphere during BRK-Ss. The balance between RH and vertical velocity is critical in deciding the PS and CI over the selected areas during ACT and BRK-Ss. An updraft with higher RH is observed over BOB, IGP, Central-India, and S-WHF during ACT-Ss. The opposite characteristics are observed over WGs, and a higher RH with a higher updraft is observed during BRK-Ss. The RH-vertical velocity joint histogram shows a broad spectrum width during ACT-Ss compared with BRK-Ss. It shows that even the lower RH can be lifted at higher altitudes due to updraft during the ACT-Ss compared with BRK-Ss. A separate analysis of TRMM and GPM shows that in the last decade, there has been an increase in the deep convective systems during the BRK-Ss, especially over the WGs and Southern India, the Tropical Ocean, and must be investigated in the future.