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A Baroclinic Laminar State for Rotating Stratified Flows

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  • 1 Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
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Abstract

A baroclinic laminar model is developed as the late-time equilibrium state in the free decay of rotating stratified turbulence under low-Froude-number scaling. Vertical motions are suppressed by stratification and ambient rotation, and in the laminar end state the flow assumes a quasi-two-dimensional form. Geometric analyses of this nonlinear conservative model reveal an f-plane baroclinic topology characterized by vertical alignment, vanishing nonlinearity, and the complete absence of helicity. Equivalent-barotropic flow is the only nonunique baroclinic solution, and its horizontal topology is restricted to a unidirectional jet and a circular vortex. Such a depleted geometry results from the constraint of basic equations where density is advected as an active scalar. It provides a baroclinic mechanism for the formation of coherent structures in geophysical flows.

Corresponding author address: Che Sun, Institute of Oceanology, 7 Nanhai Road, Qingdao, China. Email: csun@ms.qdio.ac.cn

Abstract

A baroclinic laminar model is developed as the late-time equilibrium state in the free decay of rotating stratified turbulence under low-Froude-number scaling. Vertical motions are suppressed by stratification and ambient rotation, and in the laminar end state the flow assumes a quasi-two-dimensional form. Geometric analyses of this nonlinear conservative model reveal an f-plane baroclinic topology characterized by vertical alignment, vanishing nonlinearity, and the complete absence of helicity. Equivalent-barotropic flow is the only nonunique baroclinic solution, and its horizontal topology is restricted to a unidirectional jet and a circular vortex. Such a depleted geometry results from the constraint of basic equations where density is advected as an active scalar. It provides a baroclinic mechanism for the formation of coherent structures in geophysical flows.

Corresponding author address: Che Sun, Institute of Oceanology, 7 Nanhai Road, Qingdao, China. Email: csun@ms.qdio.ac.cn

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