Schneider, Tapio and Held, Isaac M. and Garner, Stephen T. (2003) Boundary effects in potential vorticity dynamics. Journal of the Atmospheric Sciences, 60 (8). pp. 1024-1040. ISSN 0022-4928 http://resolver.caltech.edu/CaltechAUTHORS:SCHNjas03
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Many aspects of geophysical flows can be described compactly in terms of potential vorticity dynamics. Since potential temperature can fluctuate at boundaries, however, the boundary conditions for potential vorticity dynamics are inhomogeneous, which complicates considerations of potential vorticity dynamics when boundary effects are dynamically significant. A formulation of potential vorticity dynamics is presented that encompasses boundary effects. It is shown that, for arbitrary flows, the generalization of the potential vorticity concept to a sum of the conventional interior potential vorticity and a singular surface potential vorticity allows one to replace the inhomogeneous boundary conditions for potential vorticity dynamics by simpler homogeneous boundary conditions (of constant potential temperature). Functional forms of the surface potential vorticity are derived from field equations in which the potential vorticity and a potential vorticity flux appear as sources of flow quantities in the same way in which an electric charge and an electric current appear as sources of fields in electrodynamics. For the generalized potential vorticity of flows that need be neither balanced nor hydrostatic and that can be influenced by diabatic processes and friction, a conservation law holds that is similar to the conservation law for the conventional interior potential vorticity. The conservation law for generalized potential vorticity contains, in the quasigeostrophic limit, the well-known dual relationship between fluctuations of potential temperature at boundaries and fluctuations of potential vorticity in the interior of quasigeostrophic flows. A nongeostrophic effect described by the conservation law is the induction of generalized potential vorticity by baroclinicity at boundaries, an effect that plays a role, for example, in mesoscale flows past topographic obstacles. Based on the generalized potential vorticity concept, a theory is outlined of how a wake with lee vortices can form in weakly dissipative flows past a mountain. Theoretical considerations and an analysis of a simulation show that a wake with lee vortices can form by separation of a generalized potential vorticity sheet from the mountain surface, similar to the separation of a friction-induced vorticity sheet from an obstacle, except that the generalized potential vorticity sheet can be induced by baroclinicity at the surface.
|Additional Information:||©2003 American Meteorological Society. Manuscript received December 19, 2001, in final form August 30, 2002. We thank Richard Rotunno, Vanda Grubiši, and Piotr Smolarkiewicz for their willingness to share their simulation data; Piotr Smolarkiewicz for making the data available in a format convenient for us; Robert Hallberg, Peter Haynes, David Marshall, Olivier Pauluis, and Richard Rotunno for helpful comments on drafts of this paper; and Heidi Swanson for editing the manuscript. Parts of this paper where drafted while T. Schneider was with the Atmospheric and Oceanic Sciences Program at Princeton University, where he was supported by a NASA Earth System Science Fellowship.|
|Subject Keywords:||PAST 3-DIMENSIONAL OBSTACLES; GENERATED LEE VORTICES; SLIP STRATIFIED FLOW; VORTEX FORMATION; ISOLATED MOUNTAIN; LINEAR-THEORY; CIRCULATION; RIDGES; WAKES; FLUX|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Lindsay Cleary|
|Deposited On:||09 Jan 2007|
|Last Modified:||26 Dec 2012 09:29|
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