Moisture source identification for precipitation associated with tropical cyclone development over the Indian Ocean: a Lagrangian approach

In this study, we investigated the moisture sources for precipitation through a Lagrangian approach during the genesis, intensification, and dissipation phases of all tropical cyclones (TCs) that occurred over the two hemispheric sub-basins of the Indian Ocean (IO) from 1980 to 2018. In the North IO (NIO), TCs formed and reached their maximum intensity on both sides of the Indian Peninsula, to the east in the Bay of Bengal (BoB), and to the west in the Arabian Sea (AS). The oceanic areas where TCs occurred were their main moisture sources for precipitation associated with TCs. Additionally, for TCs over the BoB, continental sources from the Ganges River basin and the South China Sea also played a notable role; for TCs over the AS, the Somali Low-Level jet (along the African coast in a northerly direction) also acted as an essential moisture transport. In the South IO (SIO), the western, central, and eastern basins were identified as the preferred areas for the genesis and development of TCs. During TC activity, the central IO and the Wharton and Perth basins mostly supplied atmospheric moisture. The Mascarene High circulation was the main moisture transport mechanism for the precipitation of TCs formed in the SIO basin. In both basins, during their intensification process, TCs gained more moisture (even more intensely when reaching the hurricane category) than during the genesis or dissipation stages. Additionally, the modulation during monsoonal seasons of the moisture contribution to the TCs was more noticeable over the NIO basin than for the SIO. Overall, the moisture uptake for precipitation from the sources for TCs occurred slightly faster in the NIO basin than in the SIO basin.