Role of Bay of Bengal low‐pressure systems in the formation of mid‐tropospheric cyclones over the Arabian Sea and western India

Abstract

Arabian Sea mid‐tropospheric cyclones (MTCs), responsible for extreme rainfall events in Western India, often coincide with monsoon low‐pressure systems (LPSs) over the Bay of Bengal. However, the influence of Bay of Bengal LPSs on the formation of Arabian Sea MTCs remains unclear. This study utilizes the Weather Research and Forecasting Model (WRF) to investigate the atmospheric connection between these two basins. By introducing a balanced bogus vortex over the Bay of Bengal, cyclonic systems are induced over the Arabian Sea in the majority of ensemble members, exhibiting characteristics consistent with observations. In particular, as the Bay of Bengal vortex moves westward, the middle tropospheric trough deepens, horizontal wind shear increases, the low‐level Arabian Sea stable inversion layer weakens, and the middle troposphere moisture content over Western India and the northeast Arabian Sea rises. Subsequently, MTC genesis occurs over the northeast Arabian Sea along the western edge of the trough within 2–4 days of model integration. A vorticity budget analysis highlights the critical role of vorticity advection and tilting during the initial 24 h of MTC genesis, while vortex stretching becomes the dominant vorticity source during rapid intensification. To substantiate these findings further, a mechanism denial experiment is conducted using a real‐world instance of a coexistent Arabian Sea MTC and Bay of Bengal LPS, replicated in the model. In this experiment, conditions unfavorable for LPS genesis are created by cooling and drying the Bay of Bengal. The results demonstrate that the absence or reduced intensity of the Bay of Bengal LPS inhibits formation of the Arabian Sea MTC. In all, this study presents compelling evidence for the significant influence of Bay of Bengal low‐pressure systems on the formation of severe weather‐inducing MTCs over the Arabian Sea and Western India.