Changes in Monsoon Storm Under Extreme Sea Surface Warming

Changes in Monsoon Storm Under Extreme Sea Surface Warming 

 

Rising global temperatures have become a serious concern in the 21st century. As a result, the intensity and frequency of extreme weather events have increased worldwide. This study examines anomalies in Sea Surface Temperature (SST) in the Bay of Bengal (BoB), identified as Marine Heat Waves (MHWs), and their influence on the synoptic-scale atmospheric vortex, using satellite-derived SST observations and atmospheric reanalysis data spanning 1982-2022.

The regions that frequently experience marine heatwaves (MHWs) closely correspond with areas where the Monsoon Low-Pressure Systems (LPS) — common atmospheric vortices during the boreal summer monsoon — originate, typically occurring during the latter half of the MHW life cycle. While widespread studies have examined MHWs and monsoon systems independently, the coupled interactions between these phenomena in the Bay of Bengal remain poorly understood, despite the region's vulnerability to the impacts of extreme weather.

The presence of MHWs during the genesis phase of Monsoon Depressions (MDs), the intense monsoon LPS, appears to intensify as it modifies the pressure gradient, wind, and rainfall distributions. MDs forming under MHW conditions tend to be more intense, faster-moving, and associated with stronger winds and enhanced precipitation. Furthermore, an increase in Extreme Rainfall Events (EREs) is observed in these MHW-influenced MDs, with most EREs concentrated in the southwest quadrant of the systems. Underlying environmental conditions that could modulate this variability were analyzed using empirical indices to quantify the major mechanisms at play. The analysis reveals absolute vorticity and relative humidity as the two dominant factors contributing to MD intensification through MHWs. These analyses provide insights into how MHWs modify the background state of the atmosphere and ocean.