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Dritschel2007-JFluidMech570-Persistence.pdf1.12 MBAdobe PDFView/Open
Title: The persistence of balance in geophysical flows
Authors: Dritschel, David Gerard
Viudez, A
Keywords: Potential vorticity inversion
Gravity-wave generation
QA Mathematics
Issue Date: 10-Jan-2007
Citation: Dritschel , D G & Viudez , A 2007 , ' The persistence of balance in geophysical flows ' Journal of Fluid Mechanics , vol 570 , pp. 365-383 . , 10.1017/S0022112006002990
Abstract: Rotating stably stratified geophysical flows can exhibit a near 'balanced' evolution controlled by the conservative advection of a single scalar quantity, the potential vorticity (PV). This occurs frequently in the Earth's atmosphere and oceans where motions tend to be weak compared with the background planetary rotation and where stratification greatly inhibits vertical motion. Under these circumstances, both high-frequency acoustic waves and lower-frequency inertia-gravity waves (IGWs) contribute little to the flow evolution compared with the even-lower-frequency advection of PV. Moreover, this 'slow' PV-controlled balanced evolution appears unable to excite these higher-frequency waves in any significant way-i.e. balance persists. The present work pushes the limits of balance by systematically exploring the evolution of a range of highly nonlinear flows in which motions are comparable with the background rotation. These flows do not possess a frequency separation between PV advection and IGWs. Nonetheless, the flows exhibit a remarkable persistence of balance. Even when flows are not initialized to minimize the amount of IGWs initially present, and indeed even when flows are deliberately seeded with significant IGW amplitudes, the flow evolution-over many inertial periods (days)-remains strongly controlled by PV advection.
Version: Publisher PDF
Description: This paper introduces a novel, powerful way to understand the why geophysical flows are largely under the control of a single scalar field, the potential vorticity, a materially conserved dynamical tracer in the absence of viscous and diabatic effects.
Status: Peer reviewed
ISSN: 0022-1120
Type: Journal article
Rights: (c)2007 Cambridge University Press
Appears in Collections:University of St Andrews Research
Applied Mathematics Research

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