  $ $From June--September, the summer monsoon current (SMC) flows eastward
south of Sri Lanka and bends northeastward to form a swift jet that enters the
Bay of Bengal (BoB). As such, it is a crucial part of the water exchange
between the Arabian Sea (AS) and BoB. The processes that determine the
evolution, intensification and meandering of the SMC are only partly
understood. They involve both local and remote forcing by the wind, as well as
interactions with westward-propagating Rossby waves and eddies. In this study,
we investigate these processes using an Indian-Ocean general circulation model
(MOM4p1) that is capable of simulating the SMC realistcally. Because eddies and
meanders are smoothed out in the climatology, our analyses focus on a single
year of 2009, a period when a strong anticyclonic bend in the SMC was observed.
An eddy-kinetic-energy budget analysis shows the region to be a zone of
significant eddy activity, where both barotropic and baroclinic instabilities
are active. Based on the analysis, we classify the evolution of SMC into stages
of onset, intensification, anticyclonic bend, anticyclonic vortex formation,
meandering and termination. In addition, analysis of eddy-potential-vorticity
flux and eddy-enstrophy decay reveal when, where, and how the eddies tend to
drive the mean flow. Rossby waves and westward-propagating eddies arriving from
the east energize the SMC in June and accelerate the mean flow through an
up-gradient eddy-potential-vorticity flux. At the same time, local winds also
strengthen the flow, by increasing its mean, near-surface, kinetic energy and
raising isopycnals, the latter building up available potential energy (APE).
The baroclinic instability that takes place in late--July and early--August
releases APE, thereby generating the SMC meanders.

Atmospheric and Oceanic Physics