Wind‐driven lateral circulation in a stratified estuary and its effects on the along‐channel flow

American Geophysical Union (AGU) - Tập 117 Số C9 - 2012
Yun Li, Ming Li

Tóm tắt

In the stratified rotating estuary of Chesapeake Bay, the Ekman transport drives a counterclockwise lateral circulation under down‐estuary winds and a clockwise lateral circulation under up‐estuary winds (looking into estuary). The clockwise circulation is about twice as strong as the counterclockwise circulation. Analysis of the streamwise vorticity equation reveals a balance among three terms: titling of the planetary vorticity by vertical shear in the along‐channel current, baroclinic forcing due to sloping isopycnals at cross‐channel sections, and turbulent diffusion. The baroclinic forcing is highly asymmetric between the down‐ and up‐estuary winds. While the counter‐clockwise lateral circulation tilts isopycnals vertically and creates lateral barolinic pressure gradient to oppose the Ekman transport under the down‐estuary wind, the clockwise circulation initially flattens the isopycnals and the baroclinic forcing reinforces the Ekman transport under the up‐estuary wind. The Coriolis acceleration associated with the lateral flows is of the first‐order importance in the along‐channel momentum balance. It has a sign opposite to the stress divergence in the surface layer and the pressure gradient in the bottom layer, thereby reducing the shear in the along‐channel current. Compared with the non‐rotating system, the shear reduction is about 30–40%. Two summary diagrams are constructed to show how the averaged streamwise vorticity and along‐channel current shear vary with the Wedderburn (W) and Kelvin (Ke) numbers.

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American Geophysical Union (AGU)

Tập 117 Số C9

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