Potential vorticity redistribution by localised transient forcing in the shallow-water model
File(s)
Accepted version
Author(s)
Haigh, Michael C
Berloff, Pavel S
Type
Journal Article
Abstract
This study is motivated by the need to develop stochastic parameterisations for representing the effects of mesoscale oceanic eddies in non-eddy-resolving and eddy-permitting ocean circulation models. A necessary logical step on the way to such parameterisations is the understanding of flow responses to spatially stationary and localised, time-dependent ‘plunger’ forcings intended to represent transient eddy flux divergences. Specifically, this study develops an understanding of the plunger-induced convergence of potential vorticity (PV) fluxes using the linearised single-layer shallow-water model. Time-periodic solutions are obtained and the ‘footprint’, defined as the time-mean, quasi-linear PV flux convergence, quantifies the cumulative PV redistribution induced by the plunger. Using the footprint, the equivalent eddy flux (EEF) is defined such that it succinctly quantifies the extent of the PV redistribution, and its dependencies on the forcing latitude and the background flow are examined in detail. For a uniform background flow the EEF is positive for all forcing latitudes, corresponding to net-poleward PV flux convergence, as expected by current theory of -plane Rossby waves. The EEF also has a robust dependence on the direction and magnitude of a uniform background flow, which is a useful quality for the EEF to provide a basis for a parameterisation of eddy PV fluxes. We also examine the PV redistribution due to forcing on top of a Gaussian jet background flow and find that forcing proximity to the jet core is the primary factor in determining whether the jet is sharpened or broadened.
Date Issued
2018-10-10
Date Acceptance
2018-07-05
Citation
Journal of Fluid Mechanics, 2018, 852, pp.199-225
ISSN
0022-1120
Publisher
Cambridge University Press (CUP)
Start Page
199
End Page
225
Journal / Book Title
Journal of Fluid Mechanics
Volume
852
Copyright Statement
© 2018 Cambridge University Press. This paper has been accepted for publication and will appear in a revised form, subsequent to peer-review and/or editorial input by Cambridge University Press.
Sponsor
Natural Environment Research Council (NERC)
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000440670900003&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Grant Number
NE/R011567/1
Subjects
Science & Technology
Technology
Physical Sciences
Mechanics
Physics, Fluids & Plasmas
Physics
geophysical and geological flows
ocean circulation
shallow water flows
OCEAN CIRCULATION
EDDY FLUXES
SPECTRAL-ANALYSIS
PART I
EDDIES
DRIVEN
PARAMETERIZATION
WAVES
FLOWS
Publication Status
Published
Article Number
547
Date Publish Online
2018-08-03