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contributor authorFan Xu
contributor authorZhao Jing
contributor authorPeiran Yang
contributor authorShenghui Zhou
date accessioned2023-04-12T18:37:51Z
date available2023-04-12T18:37:51Z
date copyright2022/11/11
date issued2022
identifier otherJPO-D-21-0263.1.pdf
identifier urihttp://yetl.yabesh.ir/yetl1/handle/yetl/4289990
description abstractGeostrophic stress caused by a strong horizontal density gradient embedded in the surface boundary layer plays an important role in generating vertical motion and associated tracer transport. However, dependence of this frictionally driven vertical velocity on the Ekman number (Ek), a key dimensionless parameter for frictional flows in a rotating reference frame, has not been systematically analyzed, especially for a finite Ek. In this study, we theoretically demonstrate that the geostrophic stress always induces an ageostrophic stress acting to offset itself, and such an offsetting effect becomes more evident with increasing Ek. When Ek approaches unity or larger, vertical motion driven by geostrophic stress is much weaker than that derived by Garrett and Loder (GL81), who neglect effects of ageostrophic stress and predict a vertical velocity magnitude scaled with curl of geostrophic stress. Although the cancellation tendency between geostrophic and ageostrophic stress is universal, its underlying dynamics depends on vertical structures of turbulent viscosity and geostrophic flows. A realistic simulation in the winter Kuroshio Extension is conducted to validate the theoretical results and examine which regime, a small versus finite Ek, is more relevant in this region. It is found that the characteristic vertical scale involved in the definition of Ek is primarily determined by the vertical structure of turbulent viscosity and evidently smaller than that of geostrophic flow. The value of Ek in the winter Kuroshio Extension is generally larger than unity. Correspondingly, the GL81 model results in severe overestimation of the geostrophic stress-driven vertical velocity and tracer transport.
publisherAmerican Meteorological Society
titleVertical Motions Driven by Geostrophic Stress in Surface Boundary Layer under a Finite Ekman Number Regime
typeJournal Paper
journal volume52
journal issue12
journal titleJournal of Physical Oceanography
identifier doi10.1175/JPO-D-21-0263.1
journal fristpage3033
journal lastpage3047
page3033–3047
treeJournal of Physical Oceanography:;2022:;volume( 052 ):;issue: 012
contenttypeFulltext


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