Suppression of Baroclinic Instability in Horizontally Sheared Flows

James, I. N.

doi:10.1175/1520-0469(1987)044<3710:sobiih>2.0.co;2

Cited by 179 publications

(142 citation statements)

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“…While this theory can give information on the formation of the nonlinear energy cascade, it cannot characterize interactions of the wave field with a mean flow. Some extensions that consider nonlocal interactions and the development of zonal flows have been proposed to address this, and are specially relevant in the context of quasi-geostrophic turbulence [33], and plasma turbulence in tokamaks [34,35] to explain the development of large-scale flows.…”

Section: Introductionmentioning

confidence: 99%

Absorption of waves by large-scale winds in stratified turbulence

Leoni

Mininni

2015

Phys. Rev. E

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The atmosphere is a nonlinear stratified fluid in which internal gravity waves are present. These waves interact with the flow, resulting in wave turbulence that displays important differences with the turbulence observed in isotropic and homogeneous flows. We study numerically the role of these waves and their interaction with the large scale flow, consisting of vertically sheared horizontal winds. We calculate their space and time resolved energy spectrum (a four-dimensional spectrum), and show that most of the energy is concentrated along a dispersion relation that is Doppler shifted by the horizontal winds. We also observe that when uniform winds are let to develop in each horizontal layer of the flow, waves whose phase velocity is equal to the horizontal wind speed have negligible energy. This indicates a nonlocal transfer of their energy to the mean flow. Both phenomena, the Doppler shift and the absorption of waves traveling with the wind speed, are not accounted for in current theories of stratified wave turbulence.

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Section: Introductionmentioning

confidence: 99%

Absorption of waves by large-scale winds in stratified turbulence

Leoni

Mininni

2015

Phys. Rev. E

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“…In general, there is a projection on the barotropic mode as well when the zonal mean flow is more complex (see e.g. (James 1987), who examined the influence of barotropic shear on baroclinic instability). It appears that the instability precedes the growth in the eddy energy components, but in fact it occurs after these components have already grown significantly (this is shown below in detail).…”

Section: A Characteristic Simulationmentioning

confidence: 99%

On the energetics of a two-layer baroclinic flow

Jougla

Dritschel

2017

J. Fluid Mech.

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The formation, evolution and co-existence of jets and vortices in turbulent planetary atmospheres is examined using a two-layer quasi-geostrophic β-channel shallow water model. The study in particular focuses on the vertical structure of jets. Following Panetta & Held (1988), a vertical shear arising from latitudinal heating variations is imposed on the flow and maintained by thermal damping. Idealised convection between the upper and lower layers is implemented by adding cyclonic/anti-cyclonic pairs, called hetons, to the flow, though the qualitative flow evolution is evidently not sensitive to this or other small-scale stochastic forcing. A very wide range of simulations have been conducted. A characteristic simulation which exhibits alternation between two different phases, quiescent and turbulent, is examined in detail. We study the energy transfers between different components and modes, and find the classical picture of barotropic/baroclinic energy transfers to be too simplistic. We also discuss the dependence on thermal damping and on the imposed vertical shear. Both have a strong influence on the flow evolution. Thermal damping is a major factor affecting the stability of the flow while vertical shear controls the number of jets in the domain, qualitatively through the Rhines scale L Rh = U/β.

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“…Reduction in baroclinic growth rate in the presence of lateral barotropic shear is a somewhat general phenomenon, often called barotropic governor effect (James & Gray 1986;James 1987). James (1987) attributes the effect to the horizontal shear of advection.…”

Section: Normal Modesmentioning

confidence: 99%

“…James (1987) attributes the effect to the horizontal shear of advection. To remain in phase in the cross-flow direction in the presence of advective shear, the unstable eigenmodes are tilted in the horizontal plane and have a reduced cross-flow extent.…”

Section: Normal Modesmentioning

confidence: 99%

Baroclinic instability of axially symmetric flow over sloping bathymetry

2016

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Observations and models of deep ocean boundary currents show that they exhibit complex variability, instabilities and eddy shedding, particularly over continental slopes that curve horizontally, for example around coastal peninsulas. In this article the authors investigate the source of this variability by characterizing the properties of baroclinic instability in mean flows over horizontally curved bottom slopes. The classical 2-layer quasi-geostrophic solution for linear baroclinic instability over sloping bottom topography is extended to the case of azimuthal mean flow in an annular channel. To facilitate comparison with the classical straight channel instability problem of uniform mean flow, the authors focus on comparatively simple flows in an annulus, namely uniform azimuthal velocity and solid-body rotation. Baroclinic instability in solid-body rotation flow is analytically analogous to the instability in uniform straight channel flow due to several identical properties of the mean flow, including vanishing strain rate and vorticity gradient. The instability of uniform azimuthal flow is numerically similar to straight channel flow instability as long as the mean barotropic azimuthal velocity is zero. Nonzero barotropic flow generally suppresses the instability via horizontal curvatureinduced strain and Reynolds stresses work. An exception occurs when the ratio of the bathymetric to isopycnal slopes is close to (positive) one, as is often observed in the ocean, in which case the instability is enhanced. A non-vanishing mean barotropic flow component also results in a larger number of growing eigenmodes and in increased non-normal growth. The implications of these findings for variability in deep western boundary currents are discussed.

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Suppression of Baroclinic Instability in Horizontally Sheared Flows

Cited by 179 publications

References 0 publications

Absorption of waves by large-scale winds in stratified turbulence

Absorption of waves by large-scale winds in stratified turbulence

On the energetics of a two-layer baroclinic flow

Baroclinic instability of axially symmetric flow over sloping bathymetry

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