D. Chaudhuri, D. Sengupta, E. D’Asaro, J. Farrar, Manikandan Mathur, Sundar Ranganathan
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Near-inertial response of a salinity-stratified ocean
We study the near-inertial response of the salinity-stratified north Bay of Bengal to monsoonal wind forcing using six years of hourly observations from four moorings. The mean annual energy input from surface winds to near-inertial mixed-layer currents is 10–20 kJ/m2, occurring mainly in distinct synoptic “events” from April to September. A total of fifteen events are analyzed: Seven when the ocean is capped by a thin layer of low-salinity river water (fresh) and eight when it is not (salty). The average near-inertial energy input from winds is 40% higher in the fresh cases than in the salty cases. During the fresh events, (A) mixed layer near-inertial motions decay about two times faster, and (B) near-inertial kinetic energy below the mixed layer is reduced by at least a factor of three relative to the salty cases. The near-inertial horizontal wavelength was measured for one fresh and one salty event; the fresh was about three times shorter initially. A linear model of near-inertial wave propagation tuned to these data reproduces (B); the thin (10 m) mixed layers during the fresh events excite high modes, which propagate more slowly than the low modes excited by the thicker (40 m) mixed layers in the salty events. The model does not reproduce (A); the rapid decay of the mixed layer inertial motions in the fresh events is not explained by linear wave propagation at the resolved scales; a different and currently unknown set of processes is likely responsible.
期刊介绍:
The Journal of Physical Oceanography (JPO) (ISSN: 0022-3670; eISSN: 1520-0485) publishes research related to the physics of the ocean and to processes operating at its boundaries. Observational, theoretical, and modeling studies are all welcome, especially those that focus on elucidating specific physical processes. Papers that investigate interactions with other components of the Earth system (e.g., ocean–atmosphere, physical–biological, and physical–chemical interactions) as well as studies of other fluid systems (e.g., lakes and laboratory tanks) are also invited, as long as their focus is on understanding the ocean or its role in the Earth system.