Investigation about the cause of the intense pre-monsoon cyclonic system over the Bay of Bengal

Abstract

A 41-year dataset from 1982 to 2022 analyzed climatic patterns influencing cyclone formation in the Bay of Bengal (BoB). Results showed a significant increase in sea surface temperature (SST) and a warming trend over the past four decades. Specific humidity increased while wind shear decreased. The moisture budget showed increased precipitation and evaporation rates, possibly due to more warming scenarios. Tropical Cyclones (TC) experienced significant increases in SST anomalies. These anomalies were higher during cyclonic than non-cyclonic years, except for 2015, due to El Niño conditions. Tropical Cyclone Heat Potential (TCHP) values increased in cyclonic years, while specific humidity (SH) anomalies increased 10–15 days before cyclone formation. Moist static energy (MSE) values increased across the BoB region, with TCs Amphan, Yaas, and Asani exhibiting significant positive relative vorticity (RV) anomalies. The Madden-Julian Oscillation (MJO) plays a crucial role in TC initiation and intensification, with recent TC demonstrating this. In general, the Empirical Orthogonal Function (EOF) analysis of SST, upper-level moisture, and low wind shear for May over the BoB reveals more conducive conditions for TC intensification. Furthermore, it is also found that the negative phase of the Indian Ocean Dipole (NIOD) associated pre-monsoon month of May has produced more intense TCs in recent years over BoB. The findings of this study will facilitate augmenting existing knowledge and understanding about the genesis and intensification of pre-monsoon TCs over BoB.