High-Resolution Simulation of the Bay of Bengal Rain Plume

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 $\sim$20 m. Within the rain plume, the salinity was fresher by $\sim$4 psu, the temperature cooler by $\sim 1.5°$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 $\sim$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.