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Ocean Dynamics

, Volume 61, Issue 9, pp 1345–1368 | Cite as

Frontal circulation induced by up-front and coastal downwelling winds

  • Yu-Lin Chang
  • Lie-Yauw OeyEmail author
Article
Part of the following topical collections:
  1. Topical Collection on 2nd International Workshop on Modelling the Ocean 2010

Abstract

Two-dimensional (cross-shelf and depth) circulation by downwelling wind in the presence of a prograding front (with isopycnals that slope in the same direction as the topographic slope) over a continental shelf is studied using high-resolution numerical experiments. The physical process of interest is the cross-shelf circulation produced by northeasterly monsoon winds acting on the Kuroshio front over the East China Sea outer shelf and shelfbreak where upwelling is often observed. However, a general problem is posed and solved by idealized numerical and analytical models. It is shown that upwelling is produced shoreward of the front. The upwelling is maintained by (1) a surface bulge of negative vorticity at the head of the front; (2) bottom offshore convergence beneath the front; and (3) in the case of a surface front that is thin relative to water depth, also by upwelling due to the vorticity sheet under the front. The near-coast downwelling produces intense mixing due to both upright and slant-wise convection in regions of positive potential vorticity. The analytical model shows that the size and on-shore propagating speed of the bulge are determined by the wind and its shape is governed by a nonlinear advection–dispersion equation which yields unchanging wave-form solutions. Successive bulges can detach from the front under a steady wind. Vertical circulation cells develop under the propagating bulges despite a stable stratification. These cells can have important consequences to vertical exchanges of tracers and water masses.

Keywords

Ocean fronts Wind-front interaction Coastal downwelling Upfront winds Boluses Vertical cells Ekman transport modified by vorticity 

Notes

Acknowledgments

We thank the two anonymous reviewers and editor Dr. Hua Wang for help in improving the manuscript. YLC received a fellowship from the Graduate Student Study Abroad Program (NSC97-2917-I-003-103) of the National Science Council of Taiwan. LYO is grateful to supports by the Minerals Management Service contract number M09PS20004.

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.Department of Earth SciencesNational Taiwan Normal UniversityTaipeiTaiwan
  2. 2.Program in Atmospheric and Oceanic SciencesPrinceton UniversityPrincetonUSA

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