Barotropic Vortex Stability to Perturbations from Axisymmetry

Carr, Lester E.; Williams, R. T.

doi:10.1175/1520-0469(1989)046<3177:bvstpf>2.0.co;2

Cited by 83 publications

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“…Another difference between the two simulations is that radial and vertical gradients of the system-scale angular rotation provide a hostile environment for deep convection in the 3-D model, with a corresponding tendency to strain the convective elements in the tangential direction. This process tends to damp the small-scale fluctuations over the larger-scale motions (Melander et al, 1987;Carr and Williams, 1989;Sutyrin, 1990;, Smith and Montgomery, 1995;Rozoff et al, 2006). In contrast, convection in the AX model is not damped by such a process and consequently retains a high degree of noisiness with time.…”

Section: Evolution Of Relative Vorticitymentioning

confidence: 99%

Asymmetric and axisymmetric dynamics of tropical cyclones

et al. 2013

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Abstract. We present the results of idealized numerical experiments to examine the difference between tropical cyclone evolution in three-dimensional (3-D) and axisymmetric (AX) model configurations. We focus on the prototype problem for intensification, which considers the evolution of an initially unsaturated AX vortex in gradient-wind balance on an f plane. Consistent with findings of previous work, the mature intensity in the 3-D model is reduced relative to that in the AX model. In contrast with previous interpretations invoking barotropic instability and related horizontal mixing processes as a mechanism detrimental to the spin-up process, the results indicate that 3-D eddy processes associated with vortical plume structures can assist the intensification process by contributing to a radial contraction of the maximum tangential velocity and to a vertical extension of tangential winds through the depth of the troposphere. These plumes contribute significantly also to the azimuthally averaged heating rate and the corresponding azimuthal-mean overturning circulation.The comparisons show that the resolved 3-D eddy momentum fluxes above the boundary layer exhibit counter-gradient characteristics during a key spin-up period, and more generally are not solely diffusive. The effects of these eddies are thus not properly represented by the subgrid-scale parameterizations in the AX configuration. The resolved eddy fluxes act to support the contraction and intensification of the maximum tangential winds. The comparisons indicate fundamental differences between convective organization in the 3-D and AX configurations for meteorologically relevant forecast timescales. While the radial and vertical gradients of the system-scale angular rotation provide a hostile environment for deep convection in the 3-D model, with a corresponding tendency to strain the convective elements in the tangential direction, deep convection in the AX model does not suffer this tendency. Also, since during the 3-D intensification process the convection has not yet organized into annular rings, the azimuthally averaged heating rate and radial gradient thereof is considerably less than that in the AX model. This lack of organization results broadly in a slower intensification rate in the 3-D model and leads ultimately to a weaker mature vortex after 12 days of model integration. While azimuthal mean heating rates in the 3-D model are weaker than those in the AX model, local heating rates in the 3-D model exceed those in the AX model and at times the vortex in the 3-D model intensifies more rapidly than AX. Analyses of the 3-D model output do not support a recent hypothesis concerning the key role of small-scale vertical mixing processes in the upper-tropospheric outflow in controlling the intensification process.In the 3-D model, surface drag plays a particularly important role in the intensification process for the prototype intensification problem on meteorologically relevant timescales by helping foster the organization of convection in azimu...

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Section: Evolution Of Relative Vorticitymentioning

confidence: 99%

Asymmetric and axisymmetric dynamics of tropical cyclones

et al. 2013

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“…Air within the vortex tends to be contained and sheltered from intrusion from the environment, in part due to the strong radial shear of the tangential wind. Any asymmetry that tries to invade the vortex tends to be damped by the action of differential shear: This is the so-called vortex axisymmetrisation process (Melander et al, 1987;Carr and Williams, 1989) that is a well known essential ingredient in the robustness and persistence of coherent vortex structures in quasi two-dimensional flows. This aspect has not been explicitly discussed in the studies mentioned above in this paragraph.…”

Section: Introductionmentioning

confidence: 99%

A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer

2010

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Abstract. An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the canonical problem of a TC in vertical wind shear on an f-plane. A suite of numerical experiments is performed with intense TCs in moderate to strong vertical shear. We employ a set of simplified model physics -a simple bulk aerodynamic boundary layer scheme and "warm rain" microphysics -to foster better understanding of the dynamics and thermodynamics that govern the modification of TC intensity. In all experiments the TC is resilient to shear but significant differences in the intensity evolution occur.The ventilation of the TC core with dry environmental air at mid-levels and the dilution of the upper-level warm core are two prevailing hypotheses for the adverse effect of vertical shear on storm intensity. Here we propose an alternative and arguably more effective mechanism how cooler and drier (lower θ e ) air -"anti-fuel" for the TC power machine -can enter the core region of the TC. Strong and persistent, shear-induced downdrafts flux low θ e air into the boundary layer from above, significantly depressing the θ e values in the storm's inflow layer. Air with lower θ e values enters the eyewall updrafts, considerably reducing eyewall θ e values in the azimuthal mean. When viewed from the perspective of an idealised Carnot-cycle heat engine a decrease of storm intensity can thus be expected. Although the Carnot cycle model is -if at all -only valid for stationary and axisymmetric TCs, a close association of the downward transport of low θ e into the boundary layer and the intensity evolution offers further evidence in support of our hypothesis.Correspondence to: M. Riemer (mriemer@nps.edu)The downdrafts that flush the boundary layer with low θ e air are tied to a quasi-stationary, azimuthal wave number 1 convective asymmetry outside of the eyewall. This convective asymmetry and the associated downdraft pattern extends outwards to approximately 150 km. Downdrafts occur on the vortex scale and form when precipitation falls out from sloping updrafts and evaporates in the unsaturated air below. It is argued that, to zero order, the formation of the convective asymmetry is forced by frictional convergence associated with the azimuthal wave number 1 vortex Rossby wave structure of the outer-vortex tilt. This work points to an important connection between the thermodynamic impact in the near-core boundary layer and the asymmetric balanced dynamics governing the TC vortex evolution.

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“…Moller and Montgomery (1999) and MM00 extended MK97's derivations and simulations in the 2D non-divergent model to the 2D and 3D AB model framework and confirmed the basic finding of MK97's wave-mean-flow interaction mechanism that the wave energy can be axisymmetrized into the vortex mean flow. These results from VRW perspective are consistent with other studies that vortex axisymmetrization is found to be a universal dynamic process for monopole vortices (Melander et al 1987;McCalpin 1987;Carr and Williams 1989;Sutyrin 1989;Guinn and Schubert 1993;Holland and Dietachmayer 1993;Ritchie and Holland 1993;Smith and Montgomery 1995).…”

Section: Wave-mean-flow Interaction and Tc Intensificationsupporting

confidence: 92%

Vortex Rossby Wave Propagation in Three Dimensional Tropical-Cyclone-Like Baroclinic Vortices

Goolcharan¹

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Professor Ping Zhu, Major ProfessorThis study aims to advance our understanding of the inner-core dynamics of tropical cyclones (TCs) from the perspective of vortex Rossby waves (VRWs) through investigating wave kinematics, propagation feature, and wave-mean-flow interaction in three dimensional TC-like baroclinic vortices. Using the Wenzel-Kramers-Brillouin analysis in the asymmetric balanced model framework, the generalized wave dispersion relation, group velocities, and stagnation radius/height of VRW wave-packets in both pseudo-height and isentropic coordinates are derived. It is found that the VRW dispersion relation associated with baroclinic vortices in an isentropic coordinate has the same format as that of barotropic vortices in a pseudo-height coordinate. However, baroclinicity causes the vertical wavenumber to increase, resulting in wave propagation features different from those in barotropic vortices. The stagnation radius and height are strictly constrained by the geometry of the 'critical' surface determined by the initial properties of wave-packets

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Barotropic Vortex Stability to Perturbations from Axisymmetry

Cited by 83 publications

References 0 publications

Asymmetric and axisymmetric dynamics of tropical cyclones

Asymmetric and axisymmetric dynamics of tropical cyclones

A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer

Vortex Rossby Wave Propagation in Three Dimensional Tropical-Cyclone-Like Baroclinic Vortices

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