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Numerical simulation of coastal upwelling and inerfacial instability of a rotaion and stratified fluid

Published online by Cambridge University Press:  26 April 2006

Yan Zang
Affiliation:
Environmental Fluid Mechanics Laboratory, Stanford University, CA 94305-4020, USA
Robert L. Street
Affiliation:
2Quantum Corporation, 500 McCarthy Blvd, Milpitas, CA 95035, USA

Abstract

The evolution of the coastal upwelling and interfacial instability of a stratified and rotating fluid is studied numerically by using large-eddy simulation. Upwelling is generated near the sidewall of a rotating annulus by the shear at the top. The fluid initially consists of a stably stratified ‘two-layer’ structure with a narrow interface separating the two layers. The large-scale motion of the flow is simulated by solving the time-dependent non-hydrostaic incompressible Navier-Stockes and scalar transport equations while the small-scale motion is represented by a dynamic subgrid-scale model. The upwelling process contains both stable and unstable stratification. The vertical structure of upwelling consists of a persistent primary front, a trailing mixing zone on te shore side of the front, and a temporary secondary front which leads a top inversion layer. The longshore velocity profile has two maxima which occur at the edge of the sidewall boundary layer and at the density front. The upwelled density front is unstable to azimuthal perturbations and baroclinic waves develop and grow to large amplitude. Pairs of cyclonic and anticyclonic waves appear at the front which form ‘jet-streams’. The secondary front is unstable to azimuthal perturbations. Its instability, and the associated drop of the top inversion layer, take the form of radial bands which subsequently break up into isolated patches and eventually sink. The computed values of various upwelling time and length scales are compared to and are in good agreement with past experimental data.

Type
Research Article
Copyright
© 1995 Cambridge University Press

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