4 years ago

Dynamics of Summer Monsoon Currents around Sri Lanka.

Subham Rath, P.N.Vinayachandran, J.P.McCreary, A.Behara

$ $From June--September, the summer monsoon current (SMC) flows eastward south of Sri Lanka and turns northeastward to enter into the Bay of Bengal (BoB). The SMC is crucial for understanding exchanges between Arabian sea (AS) and BoB. The SMC shows high speeds around Sri Lanka, the reasons for which are unknown. Processes involved in the interaction of westward propagating eddies with the SMC, the meandering of the current and its ultimate termination in southeast BoB are also not well understood. In this paper, we investigate the processes that determine the evolution, intensfication, and meandering of the SMC using an Indian-Ocean general circulation model (MOM4p1) and the role of local and remote forcing in modulatingthe dynamics of SMC. An eddy-kinetic-energy (EKE) budget analysis shows the region to be a zone of significant eddy activity. Both barotropic and baroclinic instability generate eddies. Based on the EKE analysis, we classify the evolution of SMC into stages of onset, intensification, anticyclonic bend, anticyclonic vortices formation, and meandering. Eddy-potential-vorticity fluxes and eddy enstrophy decay further reveal when, where, and how the eddies tend to drive the mean flow. Rossby waves and westward propagating eddies arriving from the east energise the SMC in June and induce an acceleration tendency on the mean flow through upgradient eddy potential vorticity flux. The local winds increase the mean surface kinetic energy of the SMC and raises the isopycnals, the latter building up large amount of available potential energy (APE), and thus contribute significantly in driving the mean SMC. Baroclinic instability that takes place in late July and early August associated with the release of APE flattens the isopycnals and thus weakens the SMC. Consequently, the SMC meanders in course of time and flows into southeast BoB.

Publisher URL: http://arxiv.org/abs/1711.03311

DOI: arXiv:1711.03311v1

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