Formation of an Intrathermocline Eddy Triggered by the Coastal‐Trapped Wave in the Northern Bay of Bengal

Abstract

AbstractThe present study investigates the characteristics and mechanism of intrathermocline eddy (ITE) formation in the northern Bay of Bengal (BoB) using observations from Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) buoys moored at 15°N, 12°N, and 8°N along 90°E and simulations from a high‐resolution numerical model. Among the RAMA locations, a relatively large number of anticyclonic ITEs are observed in the northern parts (15°N) compared to the other two (12°N and 8°N). The observed ITEs are characterized by a double‐convex shape of isotherms in the thermocline with a vertical extent of about 100–200 m and a positive sea level anomaly in the surface. Water mass properties show that Andaman Sea (AS) water is trapped inside the core of the ITEs. Trajectories of these ITEs (especially at 15°N) suggest that most of them originated in the vicinity of Preparis Channel, the northernmost passage between BoB and AS. Our study shows that vorticity developed downstream of Preparis Channel due to the strong subsurface flow (∼100 cm/s), which carries AS water into the BoB, results in the formation of observed anticyclonic ITE in the northern BoB. Further analysis revealed that this strong subsurface flow through the Preparis Channel is caused by the propagation of downwelling coastal‐trapped waves along the boundaries of BoB, which originates from the equatorial Indian Ocean. Our study suggests that ITEs could be an important pathway of water mass distribution in the intermediate layers in this region.