National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2020

Meridional and zonal eddy-induced heat and salt transport in the Bay of Bengal and their seasonal modulation

Perera Gonaduwage, L., G. Chen, M.J. McPhaden, T. Priyadarshana, K. Huang, and D. Wang

J. Geophys. Res., 124, doi: 10.1029/2019JC015124 (2019)

This study investigates basin and regional‐scale eddy (turbulent)‐induced heat and salt transport associated with mesoscale eddies of the Bay of Bengal (BOB). A high level of eddy‐induced transport is found in four subregions: the western boundary of the northern BOB (NB), the western BOB (WB), the southwestern BOB near Sri Lanka (SWB), and the southeastern BOB (SEB). The main seasons for eddy‐induced heat transport in the NB and SWB are identified as the presummer (March to April) and summer monsoon (May to September) seasons, whereas the postsummer monsoon season (October to November) is the main season for the WB and SEB. It is found that not only meridional but also zonal eddy‐induced transport is significant, due to the semienclosed nature of the BOB, which restricts poleward transport in the northern part of the bay. An analysis of upper‐layer eddy energetics reveals that the main contributor to the increased eddy kinetic energy and thus the transport is baroclinic instability in the NB, SWB, and WB, while both barotropic and baroclinic instability are important in the SEB. Using a 2.5‐layer reduced gravity model, baroclinic instability in the NB, SWB, and SEB is further investigated. The results reveal that strong vertical velocity shear and weak stratification are essential for generating baroclinic instability, which enhances the seasonal eddy‐induced transport in the respective subregions.

Plain Language Summary. We estimate eddy‐induced heat and salt transport in the Bay of Bengal basin to understand the general characteristics and the key process determining their spatial and seasonal distribution. A linear stability analysis of eddy energetics demonstrates that weak stratification and strong vertical velocity shear generated by the strengthening of mean zonal currents intensify baroclinic instability and enhance the eddy‐induced transport. In addition, it is found that the local wind‐stress curl and remote forcing from the equator partly contribute to the seasonal modulation of eddy‐induced heat transport.

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