Western boundary layer nonlinear control of the oceanic gyres

This study examines the influence of flow nonlinearity in western boundary layers upon the turbulent wind-driven ocean gyres. Our analysis involves comparisons between large-scale circulation properties of the linear and nonlinear states, as well as a Lagrangian particle analysis of relevant flow fe...

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Bibliographic Details
Published in:Journal of fluid mechanics 2021-05, Vol.918, Article A43
Main Authors: Kurashina, Ryosuke, Berloff, Pavel, Shevchenko, Igor
Format: Article
Language:English
Subjects:
Analysis
Anomalies
Atmospheric boundary layer
Boundary conditions
Boundary layers
Downstream effects
Enstrophy
Exchanging
Fluid dynamics
Fluxes
Friction
General circulation models
Gyres
Hypotheses
JFM Papers
Nonlinear control
Nonlinear systems
Nonlinearity
Ocean basins
Ocean circulation
Potential vorticity
Relative vorticity
Turbulent boundary layer
Turbulent wind
Vortices
Vorticity
Wind
Wind effects
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Description
Summary:This study examines the influence of flow nonlinearity in western boundary layers upon the turbulent wind-driven ocean gyres. Our analysis involves comparisons between large-scale circulation properties of the linear and nonlinear states, as well as a Lagrangian particle analysis of relevant flow features. We find that the so-called counter-rotating gyre anomalies, which are nonlinear circulation features embedded in the gyres, are consistent in shape with the linear, weakened, wind-curl response created by the geometric wind effect. However, the linear response is far too weak without considering nonlinear effects. Within the western boundary layer lobe of these features, the nonlinear boundary layer has a pivotal impact upon the global circulation. Effects of potential vorticity advection inhibit viscous relative vorticity fluxes through the western boundary. This creates a significant potential vorticity imbalance between the gyres. Consequently, this generates an accumulation of enstrophy downstream in the inertial recirculation zones, which in turn supports the eastward jet. However, within the ocean basin, the growing imbalance is eventually rectified by inter-gyre potential vorticity exchanges owing to nonlinear fluxes. The Lagrangian particle analysis reveals the inter-gyre exchange mechanism, where particles seeded within the western boundary layer migrate between the gyres and weaken the eastward jet extension.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2021.384