Dynamics of Eddy Generation in the Central Bay of Bengal

Abstract

Eddy activity in the central Bay of Bengal (BoB) is revealed using satellite observations and hydrographic data. Altimetric data show that eddies are generated near the eastern boundary, propagate southwestward, and have periods predominantly in the 30-to 120-day band. Temperature profiles from the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) buoy at 90°E, 15°N, have their highest amplitude in the depth range of the thermocline, indicating that the eddies are associated with a vertical motion of the thermocline (a first-baroclinic-mode response). To investigate the cause of the eddies, we obtained a suite of solutions to nonlinear and linear versions of a 1½-layer (reduced-gravity) model. They demonstrate that equatorial wind forcing, Myanmar bump and Andaman Island, and nonlinearity are all essential for eddy formation. Among the nonlinear terms, the advection terms are the primary cause.Plain Language Summary This study combines observations and model to understand eddy generation in the central Bay of Bengal. When equatorial wind-driven downwelling (upwelling) Kelvin waves propagate to the tip of the Irrawaddy Delta off Myanmar, anticyclonic (cyclonic) eddies are generated there that subsequently propagate southwestward. The eddies are mainly driven by equatorial zonal winds, with both nonlinearity and coastline geometry essential for eddy generation.

Thermohaline Structures and Heat/Freshwater Transports of Mesoscale Eddies in the Bay of Bengal Observed by Argo and Satellite Data

“…The number of CEs was approximately 17% higher than that of AEs, and their mean lifespans were approximately 57 days and 56 days, respectively. Consistent with previous studies [14,[16][17], eddy-rich regions with more than four CEs and AEs in each 1 ° bin were observed to be located at the western boundary, the northern bay, and the Andaman Sea (Figure 3a, b). The mean amplitudes of the CEs and AEs show a similar spatial pattern (Figure 3c,d).…”

“…In addition, another critical region for eddy generation is located at the eastern boundary over the BOB, according to altimeter measurements [14,[16][17]. The equatorial wind forcing and the instability triggered by the Myanmar bump are the two major reasons for eddy formation in that area [17].…”

“…Although a similar analysis was carried out in the western bay [27], only the vertical profiles (one−dimension) of the mean anomalies in temperature, salinity, and dynamic height inside eddies were depicted in the study, which suggests that both anticyclonic and cyclonic eddies have a single core vertical structure, with the core located at a depth of approximately 100 dbar. In another recent study [17], a truly three−dimensional thermal structure of a composite anticyclonic/cyclonic eddy over the central bay was presented for the first time and revealed the subsurface intensification of eddies. To date, a full image of the three−dimensional structures of temperature, salinity, and velocity inside eddies is still absent in the BOB.…”

Role of Andaman and Nicobar Islands in eddy formation along western boundary of the Bay of Bengal

“…Later, Cheng et al . 12 showed that the Rossby waves, radiated out from the coastal Kelvin wave, get significantly altered by the ANIs and increase eddy activity in the central BoB. But, their analysis was restricted only in the central and eastern BoB (east of 85°E).…”

Interactions Between Mesoscale Eddies and Synoptic Oscillations in the Bay of Bengal During the Strong Monsoon of 2019

“…Again, the median radius of these eddies is nearly equal for AEs and CEs (~100 km), but CEs have a much larger range reaching up to 192 km. The largest amplitude eddies tended to generate in the western Bay (Figure 1), where baroclinic instability of the EICC helps generates eddies (Cheng et al, 2018), so their trajectories follow this current (Figures 7g and 7h). In the EICC region, there is a higher concentration of AEs.…”