Merging of two-layer baroclinic vortices

1991 ◽  
pp. 355-365
Author(s):  
Jacques Verron ◽  
Emil Hopfinger ◽  
James C. McWilliams
Keyword(s):  
Baroclinic Vortices

Scale-dependent merging of baroclinic vortices

1994 ◽  
Vol 264 ◽  
pp. 81-106 ◽  
Author(s):  
J. Verron ◽  
S. Valcke
Keyword(s):  
Numerical Simulations ◽  
Critical Point ◽  
Lower Layer ◽  
Interaction Mechanism ◽  
Competitive Effects ◽  
Different Types ◽  
Shape Effects ◽  
Baroclinic Vortices ◽  
The Relationship ◽  
Stratified Model

The influence of stratification on the merging of like-sign vortices of equal intensity and shape is investigated by numerical simulations in a quasi-geostrophic, two-layer stratified model. Two different types of vortices are considered: vortices defined as circular patches of uniform potential vorticity in the upper layer but no PV anomaly in the lower layer (referred to as PVI vortices), and vortices defined as circular patches of uniform relative vorticity in the upper layer but no motion in the lower layer (referred to as RVI vortices). In particular, it is found that, in the RVI case, the merging behaviour depends strongly on the magnitude of the stratification (i.e. the ratio of internal Rossby radius and vortex radius). The critical point here appears to be whether or not the initial eddies have a deep flow signature in terms of PV.The specific phenomenon of scale-dependent merging observed is interpreted in terms of the competitive effects of hetonic interaction and vortex shape. In the case of weaker stratification, the baroclinic structure of the eddies can be seen as dominated by a mechanism of hetonic interaction in which bottom flow appears to counteract the tendency of surface eddies to merge. In the case of larger stratification, the eddy interaction mechanism is shown to be barotropically dominated, although interface deformation still determines the actual eddy vorticity profile during the initialization stage. Repulsion (hetonic) effect therefore oppose attraction (barotropic shape) effects in a competitive process dependent on the relationship between the original eddy lengthscale and the first internal Rossby radius.A concluding discussion considers the implications of such analysis for real situations, in the ocean or in the laboratory.

scholarly journals Influence of Bottom Topography on Vortex Stability

2019 ◽  
Vol 49 (12) ◽  
pp. 3199-3219 ◽  
Author(s):  
Bowen Zhao ◽  
Emma Chieusse-Gérard ◽  
Glenn Flierl
Keyword(s):  
Growth Rate ◽  
Linear Stability ◽  
Bottom Topography ◽  
Relative Vorticity ◽  
Subsequent Evolution ◽  
Vortex Stability ◽  
Number Of Layers ◽  
One Step ◽  
Baroclinic Vortices ◽  
Dynamics Simulations

AbstractThe effects of topography on the linear stability of both barotropic vortices and two-layer, baroclinic vortices are examined by considering cylindrical topography and vortices with stepwise relative vorticity profiles in the quasigeostrophic approximation. Four vortex configurations are considered, classified by the number of relative vorticity steps in the horizontal and the number of layers in the vertical: barotropic one-step vortex (Rankine vortex), barotropic two-step vortex, and their two-layer, baroclinic counterparts with the vorticity steps in the upper layer. In the barotropic calculation, the vortex is destabilized by topography having an oppositely signed potential vorticity jump while stabilized by topography of same-signed jump, that is, anticyclones are destabilized by seamounts while stabilized by depressions. Further, topography of appropriate sign and magnitude can excite a mode-1 instability for a two-step vortex, especially relevant for topographic encounters of an otherwise stable vortex. The baroclinic calculation is in general consistent with the barotropic calculation except that the growth rate weakens and, for a two-step vortex, becomes less sensitive to topography (sign and magnitude) as baroclinicity increases. The smaller growth rate for a baroclinic vortex is consistent with previous findings that vortices with sufficient baroclinic structure could cross the topography relatively easily. Nonlinear contour dynamics simulations are conducted to confirm the linear stability analysis and to describe the subsequent evolution.

Convective Flow in Baroclinic Vortices

1994 ◽  
Vol 24 (9) ◽  
pp. 1841-1849 ◽  
Author(s):  
Sergey N. Aristov ◽  
Jonas Nycander
Keyword(s):  
Convective Flow ◽  
Baroclinic Vortices

scholarly journals Tilted Baroclinic Tidal Vortices

2009 ◽  
Vol 39 (2) ◽  
pp. 333-350 ◽  
Author(s):  
Miguel Canals ◽  
Geno Pawlak ◽  
Parker MacCready
Keyword(s):  
Velocity Field ◽  
Tropical Cyclones ◽  
Density Perturbation ◽  
Density Field ◽  
Field Observations ◽  
Simple Analytical Model ◽  
Horizontal Pressure Gradient ◽  
Background Density ◽  
Horizontal Pressure ◽  
Baroclinic Vortices

Abstract The structure of baroclinic vortices generated by horizontal flow separation past a sloping headland in deep, stably stratified waters is investigated. The most distinctive feature of these eddies is that their cores are strongly tilted with respect to the stratification, yet their velocity field remains quasi-horizontal. Field observations and numerical simulations are used to explore the consequences of the strong tilt on the eddy baroclinic structure. It is found that the background density field is altered in such a way as to maintain a pressure minimum in the tilted vortex cores. This adjustment results in a fundamental asymmetry of the density field. Isopycnals are deflected upward on the shoreward side and downward on the opposite side of the eddy center. The resulting pattern closely resembles the asymmetries of azimuthal wavenumber one that develop when tropical cyclones become tilted by an environmental shear. The authors provide a simple analytical model that suggests this structure is obtained via a balance between the centrifugal force and the horizontal pressure gradient. As the eddies release from the boundary, adjust, and decay, their tilt as well as the associated density perturbation decrease and lose coherence. It is suggested that this may lead to a conversion of potential energy into kinetic energy.

Finite-amplitude evolution of two-layer geostrophic vortices

1988 ◽  
Vol 197 ◽  
pp. 331-348 ◽  
Author(s):  
Karl R. Helfrich ◽  
Uwe Send
Keyword(s):  
Initial Conditions ◽  
Lower Layer ◽  
Finite Amplitude ◽  
Supercritical Regime ◽  
Azimuthal Mode ◽  
Contour Dynamics ◽  
Barotropic Flow ◽  
Break Up ◽  
Baroclinic Vortices ◽  
Amplitude Evolution

The finite-amplitude evolution of circular two-layer quasi-geostrophic vortices with piecewise uniform potential vorticity in each layer (also termed ‘heton’ clouds by Hogg & Stommel 1985a and Pedlosky 1985) is studied using the contour dynamics method. The numerical investigations are preceded by a linear stability analysis which shows the stabilizing influence of deepening the lower layer. Net barotropic flow may be either stabilizing or destabilizing. The contour dynamics calculations for baroclinic vortices show that supercritical (i.e. linearly unstable) conditions may lead to explosive break up of the vortex via the generation of continuous hetons at the cloud boundary. The number of vortex pairs is equal to the azimuthal mode number of the initial disturbance. An additional weakly supercritical regime in which amplitude vacillation occurs, but not explosive growth, is identified. Vortices with net barotropic circulation behave similarly except that the layer with vorticity opposite to the barotropic circulation will break up first. Strong barotropic circulation can inhibit the development of hetons. The stronger layer may eject thin filaments, but remain mostly intact. Calculations for initial conditions composed of several unstable modes show that the linearly most unstable mode dominates at finite amplitude.

Stability of Baroclinic Vortices on the β Plane and Implications for Transport

2016 ◽  
Vol 46 (11) ◽  
pp. 3245-3262
Author(s):  
M. V. Rudko ◽  
I. V. Kamenkovich ◽  
D. S. Nolan
Keyword(s):  
Large Scale ◽  
Axisymmetric Flow ◽  
Bottom Layer ◽  
Wave Radiation ◽  
Mean Flow ◽  
Lagrangian Analysis ◽  
Finite Time Lyapunov Exponent ◽  
Balance Analysis ◽  
Baroclinic Vortices ◽  
Energy Balance Analysis

AbstractThis paper explores stability of and transport by baroclinic vortices on the β plane using a two-layer, quasigeostrophic model. The study adapts a wave–mean flow formalism and examines interactions between the axisymmetric flow (“the vortex”) and residuals (“the waves”). Unlike baroclinically unstable vortices on the f plane, such vortices on the β plane can be also vulnerable to barotropic instability as revealed by the globally integrated energy balance analysis. The spatial structure of energy fluxes shows the energy leakage inside the vortex core when its breakdown occurs. Mixing by stable and unstable vortical flows is quantified through the computation of finite-time Lyapunov exponent (FTLE) maps. Depending on the strength of wave radiation, the upper-layer FTLE maps of stable vortices show either an annulus or volute ring of vigorous mixing inside the vortex interior. This ring region is disrupted when the vortex becomes unstable. Both stable and unstable vortices show the wavy patterns of FTLE in the near and far fields. Despite the fact that the initial vortex resides in the top layer only, significant FTLE patterns are observed in the deep layer at later times. Lagrangian analysis of the vortex-induced change of large-scale tracer gradient demonstrates significant effects of vortex instability in the top layer and the importance of the wavelike anomalies in the bottom layer.

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