High‐Resolution Simulation of the Bay of Bengal Rain Plume

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Abstract
Rainfall plays an important role in shaping the dynamics of the ocean surface layer. However, the impact of prolonged rainfall, lasting a few days, on the Bay of Bengal's surface layer remains poorly understood. This study investigates the formation of a rain plume (low‐salinity plume) associated with a rainfall event that occurred from 22 to 31 July 2015, using a very high‐resolution (1 km) ROMS model simulation. The rain plume exhibits distinct impacts across its lifecycle, modifying upper‐ocean salinity, temperature, stratification, and the mixed layer (ML), as well as intensifying submesoscale activity. The rainfall event was associated with a cyclonic storm KOMEN. Strong wind‐driven surface currents pushed the plume southwestward from the northern bay. Afterward, offshore movement of the plume was dominated by geostrophic currents. By August 2, it reached maximum intensity, forming a mushroom‐like shape approximately 140 km in length, 37 km in width, and a depth of 20 m. Within the rain plume, the salinity was fresher by 4 psu, the temperature cooler by C, and the ML vanished. The temporal evolution of the ML within the rain plume led to three distinct phases: deepening, steady, and shallowing. Our findings also highlight enhanced submesoscale activity along the edges of the rain plume. The life cycle of the rain plume lasted 13 days from formation, intensification, to dissipation. These findings enhance the understanding of upper‐ocean responses to freshwater plumes and highlight the role of high‐resolution models in capturing them, with implications to intense weather systems and marine ecosystem.

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