The Role of Tropical Easterly Jet on the Bay of Bengal’s Tropical Cyclones: Observed Climatology and Future Projection
Abdullah Al Fahad, Oreste Reale, Andrea Molod, Tahmidul Azom Sany, Md Tashin Ahammad, Dimitris Menemenlis
Abstract
Abstract Tropical cyclones (TCs) in the Bay of Bengal (BoB) are among the most devastating events in nature, significantly influencing human life. They affect the region between April and December, being separated into two distinct phases: the premonsoon (April–June, AMJ) and postmonsoon (October–December, OND), with little activity during the monsoon peak. In this article, the influence of the tropical easterly jet (TEJ) on the observed BoB TC activity, and the expected changes under global warming conditions, are investigated using reanalyses and Coupled Model Intercomparison Project phase 6 (CMIP6) models. The general assumption is that TC activity should increase in response to warmer sea surface temperature (SST). However, several dynamical processes are needed to create organized convection, which is a prerequisite for TC development. The results show that the frequency and accumulated energy should decrease in the future (2020–49), compared to the historical climate (1950–79), during both phases. However, the northern BoB TCs’ intensity increases during OND. The change of the mean TEJ and intermittent shear relaxations in the future climate are found to play a major role in the change of TC activity rather than the SST. During AMJ, a southward shift of the mean TEJ and its intermittent shear relaxations are associated with reduced TC activity. During OND, the decrease of the frequency of TEJ and subtropical jet (STJ) intermittent shear relaxations are associated with the reduction of TC activity. This study clarifies the importance of both the mean and intermittency of the TEJ in determining the future of TC activity in the BoB.