scholarly journals Upgradient and Downgradient Potential Vorticity Fluxes Produced by Forced Rossby Waves. Part II: Parameter Sensitivity and Physical Interpretation

2018 ◽  
Vol 48 (5) ◽  
pp. 1211-1230 ◽  
Author(s):  
Genta Mizuta
Keyword(s):  
Potential Vorticity ◽  
Rossby Waves ◽  
Lower Layer ◽  
External Forcing ◽  
Direct Effects ◽  
Horizontal Scale ◽  
Wave Interactions ◽  
Weak Stratification ◽  
Quasigeostrophic Model ◽  
Basic Features

AbstractWe examine the potential vorticity (PV) flux produced by forced Rossby waves in a two-layer quasigeostrophic model, using a perturbation analysis. Rossby waves are excited by external forcing applied to the upper layer. The southward PV flux is produced in the lower layer by the higher-order Rossby waves that are excited by nonlinear wave–wave interactions, whereas the northward PV flux is produced in the upper layer. The direction of the PV flux is consistent with that obtained by an eddy-resolving model of the wind-driven circulation in previous studies. The southward PV flux is produced in a wide parameter range comparable to the eddy-resolving model. The basic features of the PV flux remain unchanged even in the limit of weak stratification. In this limit, stratification has nearly no effect on the flow, except that it isolates the lower layer from the direct effects of external forcing. The mechanism of the southward PV flux is explained using basic features of the barotropic Rossby waves and does not depend on details of the model. Furthermore, the resonant triad interaction of Rossby waves does not affect the PV flux. Stratification weakens or strengthens the PV flux depending on the horizontal scale of the external forcing.

scholarly journals On the Poleward Motion of Midlatitude Cyclones in a Baroclinic Meandering Jet

2013 ◽  
Vol 70 (8) ◽  
pp. 2629-2649 ◽  
Author(s):  
Ludivine Oruba ◽  
Guillaume Lapeyre ◽  
Gwendal Rivière
Keyword(s):  
Potential Vorticity ◽  
Statistical Study ◽  
Rossby Waves ◽  
Lower Layer ◽  
Finite Amplitude ◽  
Synoptic Scale ◽  
Beta Plane ◽  
The Cross ◽  
Quasigeostrophic Model ◽  
Pv Gradient

Abstract The motion of surface depressions evolving in a background meandering baroclinic jet is investigated using a two-layer quasigeostrophic model on a beta plane. Synoptic-scale finite-amplitude cyclones are initialized in the lower and upper layer to the south of the jet in a configuration favorable to their baroclinic interaction. The lower-layer cyclone is shown to move across the jet axis from its warm-air to cold-air side. It is the presence of a poleward-oriented barotropic potential vorticity (PV) gradient that makes possible the cross-jet motion through the beta-drift mechanism generalized to a baroclinic atmospheric context. The potential vorticity gradient associated with the jet is responsible for the dispersion of Rossby waves by the cyclones and the development of an anticyclonic anomaly in the upper layer. This anticyclone forms a PV dipole with the upper-layer cyclone that nonlinearly advects the lower-layer cyclone across the jet. In addition, the background deformation is shown to modulate the cross-jet advection. Cyclones evolving in a deformation-dominated environment (south of troughs) are strongly stretched while those evolving in a rotation-dominated environment (south of ridges) remain quasi isotropic. It is shown that the more stretched cyclones trigger a more efficient dispersion of energy, create a stronger upper-layer anticyclone, and move perpendicularly to the jet faster than the less stretched ones. Both the intensity and location of the upper-layer anticyclone explain the distinct cross-jet speeds. A statistical study consisting in initializing cyclones at different locations south of the jet core confirms that the cross-jet motion is faster for the more meridionally elongated cyclones evolving in areas of strongest barotropic PV gradient.

scholarly journals Upgradient and Downgradient Potential Vorticity Fluxes Produced by Forced Rossby Waves. Part I: Basic Experiments

2018 ◽  
Vol 48 (5) ◽  
pp. 1191-1209 ◽  
Author(s):  
Genta Mizuta
Keyword(s):  
Potential Vorticity ◽  
Rossby Waves ◽  
Deep Layer ◽  
Harmonic Wave ◽  
Homogenization Theory ◽  
Irreversible Processes ◽  
Harmonic Waves ◽  
External Forcing ◽  
Mean Flow ◽  
Deep Layers

AbstractThe mean flow and potential vorticity (PV) flux produced by Rossby waves are examined, particularly by focusing on the effects of stratification and nonlinearity on upgradient and downgradient PV fluxes. Rossby waves are excited by an external forcing confined near the surface and produce a northward (upgradient) PV flux in the surface layer. While the meridional PV flux is considerably weak in the deep layer in the weakly nonlinear case, the southward (downgradient) PV flux is produced as nonlinearity increases. In both the surface and deep layers, the distribution of the PV flux and mean flow is qualitatively similar to that in recirculation gyres obtained in an eddy-resolving model of the wind-driven circulation. A perturbation analysis shows that the primary and harmonic waves are excited by external forcing and wave–wave interaction between the primary waves, respectively. The meridional PV fluxes in the surface and deep layers are mostly produced by the primary and harmonic waves, respectively. The southward PV flux in the deep layer is produced by the interaction between the barotropic harmonic wave and the first baroclinic component of nonlinear forcing by the primary waves. The irreversible processes that are implicitly assumed in the PV homogenization theory (Rhines and Young) do not substantially affect the southward PV flux. The qualitative features of the PV flux remain unchanged even when nonlinearity is increased beyond the range in which the perturbation theory is exactly applicable.

scholarly journals Piecewise potential vorticity inversion without far-field response?

2020 ◽  
Author(s):  
Joseph Egger ◽  
Klaus P. Hoinka
Keyword(s):  
Boundary Conditions ◽  
Potential Vorticity ◽  
Lower Layer ◽  
Far Field ◽  
Potential Vorticity Inversion ◽  
Field Response ◽  
Quasigeostrophic Model ◽  
Physical Impact ◽  
The Impact ◽  
Field Influence

AbstractGiven a flow domain D with subdomains D1 and D2, piecewise potential vorticity inversion (PPVI) inverts a potential vorticity (PV) anomaly in D2 and assumes vanishing PV in D1 where boundary conditions must be taken into account. It is a widely held view that the PV anomaly exerts a far-field influence on D1 which is revealed by PPVI. Tests of this assertion are conducted using a simple quasigeostrophic model where an upper layer D2 contains a PV anomaly and D1 is the layer underneath. This anomaly is inverted. Any downward physical impact of PV in D2 must also be represented in the results of a downward piecewise density inversion (PDI) based on the hydrostatic relation and the density in D2 as following from PPVI. There is no doubt about the impact of the mass in D2 on the flow in the lower layer D1. Thus results of PPVI and PDI have to agree closely. First, PPVI is applied to a locally confined PV-anomaly in D2. There is no far-field ’response’ in D1 if stationarity is imposed. Modifications of boundary conditions lead to “induced” flows in D1 but the results of PPVI and PDI differ widely. This leads to a simple proof that there is no physical far-field influence of PV-anomalies in D2. Wave patterns of the streamfunction restricted to D2 are prescribed in a second series of tests. The related PV-anomalies are obtained by differentiation and are also confined to D2 in this case. This approach illustrates the basic procedure to derive PV-fields from observations which excludes a far-field response.

A Balanced Approximation of the One-Layer Shallow-Water Equations on a Sphere

2009 ◽  
Vol 66 (6) ◽  
pp. 1735-1748 ◽  
Author(s):  
W. T. M. Verkley
Keyword(s):  
Shallow Water ◽  
Potential Vorticity ◽  
Shallow Water Equations ◽  
Rossby Waves ◽  
Coriolis Parameter ◽  
Beta Plane ◽  
Propagating Waves ◽  
Barotropic Vorticity Equation ◽  
Barotropic Vorticity ◽  
The One

Abstract A global version of the equivalent barotropic vorticity equation is derived for the one-layer shallow-water equations on a sphere. The equation has the same form as the corresponding beta plane version, but with one important difference: the stretching (Cressman) term in the expression of the potential vorticity retains its full dependence on f 2, where f is the Coriolis parameter. As a check of the resulting system, the dynamics of linear Rossby waves are considered. It is shown that these waves are rather accurate approximations of the westward-propagating waves of the second class of the original shallow-water equations. It is also concluded that for Rossby waves with short meridional wavelengths the factor f 2 in the stretching term can be replaced by the constant value f02, where f0 is the Coriolis parameter at ±45° latitude.

A regime perspective on jet and blocking dynamics in CMIP6

2021 ◽  
Author(s):  
Joshua Dorrington
Keyword(s):  
Potential Vorticity ◽  
Climate Models ◽  
Rossby Waves ◽  
Climate Model ◽  
Atmospheric Dynamics ◽  
Interdecadal Variability ◽  
Model Ensemble ◽  
Atlantic Region ◽  
Non Linear ◽  
Jet Structure

<p>Weather over the Euro-Atlantic region during winter is highly variable, with rich and chaotic internal atmospheric dynamics. In particular, the non-linear breaking of Rossby waves irreversibly mixes potential vorticity contours and so triggers shifts in the latitude of the eddy driven jet and establishes persistent anticyclonic blocking events. The concept of atmospheric regimes captures the tendency for blocks – and for the jet – to persist in a small number of preferred locations. Regimes then provide a non-linear basis through which model deficiencies, interdecadal variability and forced trends in the Euro-Atlantic circulation can be studied.</p><p>A drawback of past regime approaches is that they were unable to easily capture both the dynamics of the jet and of blocking anticyclones simultaneously. In this work we apply a recently developed regime framework, which is able to capture both these important aspects while reducing sampling variability, to the CMIP6 climate model ensemble. We analyse both the historical variability and biases of blocking and jet structure in this latest generation of climate models, and make new estimates of the anthropogenic forced trend over the coming century.</p><p> </p>

scholarly journals Chaotic Behaviors in the Response of a Quasigeostrophic Oceanic Double Gyre to Seasonal External Forcing

2010 ◽  
Vol 40 (7) ◽  
pp. 1458-1472 ◽  
Author(s):  
Shinya Shimokawa ◽  
Tomonori Matsuura
Keyword(s):  
Nonlinear Oscillations ◽  
Variable Parameter ◽  
External Forcing ◽  
Strong Current ◽  
Decadal Variations ◽  
Current Region ◽  
Quasigeostrophic Model ◽  
Gyre System ◽  
Double Gyre

Abstract In an oceanic double-gyre system, nonlinear oscillations of the ocean under seasonally changing external forcing are investigated using a 1.5-layer quasigeostrophic model and a simple model related to energy balance of the oceanic double gyre. In the experiments, the variable parameter is the amplitude of external seasonal forcing and the Reynolds number is fixed as 39, at which periodic shedding of inertial subgyres occurs. The authors found that entrainment (at 2 times the period of the forcing) and intermittency (on–off type), phenomena that are often seen in nonlinear systems, emerge with increasing amplitude of the forcing. They seem to be related to the generation mechanism and characteristics of long-term (from interannual to decadal) variations in the strong current region of subtropical gyres such as the Kuroshio and its extension region.

scholarly journals Potential Vorticity of the Madden–Julian Oscillation

2012 ◽  
Vol 69 (1) ◽  
pp. 65-78 ◽  
Author(s):  
Chidong Zhang ◽  
Jian Ling
Keyword(s):  
Potential Vorticity ◽  
Diabatic Heating ◽  
Rossby Waves ◽  
Early Stage ◽  
Relative Vorticity ◽  
Dynamical Structure ◽  
Madden Julian Oscillation ◽  
Convective Envelope ◽  
Convective Initiation ◽  
Pv Generation

Abstract This study explores the extent to which the dynamical structure of the Madden–Julian oscillation (MJO), its evolution, and its connection to diabatic heating can be described in terms of potential vorticity (PV). The signature PV structure of the MJO is an equatorial quadrupole of cyclonic and anticyclonic PV that tilts westward and poleward. This PV quadrupole is closely related to positive and negative anomalies in precipitation that are in a swallowtail pattern extending eastward along the equator and splitting into off-equatorial branches westward. Two processes dominate the generation of MJO PV. One is linear, involving MJO diabatic heating alone. The other is nonlinear, involving diabatic heating and relative vorticity of perturbations spectrally outside the MJO domain but spatially constrained to the MJO convective envelope. The MJO is thus partially a self-sustaining system and partially a consequence of scale interaction of MJO-constrained stochastic processes. Convective initiation of the MJO over the Indian Ocean features a swallowtail pattern of negative anomalous precipitation and associated anticyclonic PV anomalies at the early stage, and increasing cyclonic PV generation straddling the equator in the midtroposphere due to increasing positive anomalies in precipitation. These lead to the swallowtail pattern in positive anomalous precipitation and the associated PV quadrupole that signifies the fully developed MJO. The equatorial Kelvin and Rossby waves bear PV structures distinct from that of the MJO. They contribute insignificantly to the structure and generation of MJO PV. Solely based on the PV analysis, a hypothesis is proposed that the fundamental dynamics of the MJO depends on neither Kelvin nor Rossby waves.

scholarly journals Mathematical Modeling of Vortex Interaction Using a Three-Layer Quasigeostrophic Model. Part 2: Finite-Core-Vortex Approach and Oceanographic Application

Mathematics ◽  
2020 ◽  
Vol 8 (8) ◽  
pp. 1267
Author(s):  
Mikhail A. Sokolovskiy ◽  
Xavier J. Carton ◽  
Boris N. Filyushkin
Keyword(s):  
Large Scale ◽  
Lower Layer ◽  
Middle Layer ◽  
Vortex Interaction ◽  
Vortex Dipoles ◽  
The North ◽  
Surface Cyclone ◽  
Vertical Density ◽  
Quasigeostrophic Model ◽  
The Stability

The three-layer version of the contour dynamics/surgery method is used to study the interaction mechanisms of a large-scale surface vortex with a smaller vortex/vortices of the middle layer (prototypes of intrathermocline vortices in the ocean) belonging to the middle layer of a three-layer rotating fluid. The lower layer is assumed to be dynamically passive. The piecewise constant vertical density distribution approximates the average long-term profile for the North Atlantic, where intrathermocline eddies are observed most often at depths of 300–1600 m. Numerical experiments were carried out with different initial configurations of vortices, to evaluate several effects. Firstly, the stability of the vortex compound was evaluated. Most often, it remains compact, but when unstable, it can break as vertically coupled vortex dipoles (called hetons). Secondly, we studied the interaction between a vertically tilted cyclone and lenses. Then, the lenses first undergo anticlockwise rotation determined by the surface cyclone. The lenses can induce alignment or coupling with cyclonic vorticity above them. Only very weak lenses are destroyed by the shear stress exerted by the surface cyclone. Thirdly, under the influence of lens dipoles, the surface cyclone can be torn apart. In particular, the shedding of rapidly moving vortex pairs at the surface reflects the presence of lens dipoles below. More slowly moving small eddies can also be torn away from the main surface cyclone. In this case, they do not appear to be coupled with middle layer vortices. They are the result of large shear-induced deformation. Common and differing features of the vortex interaction, modeled in the framework of the theory of point and finite-core vortices, are noted.

scholarly journals Dynamics of the Upper Oceanic Layers in Terms of Surface Quasigeostrophy Theory

2006 ◽  
Vol 36 (2) ◽  
pp. 165-176 ◽  
Author(s):  
G. Lapeyre ◽  
P. Klein
Keyword(s):  
Potential Vorticity ◽  
Surface Density ◽  
Three Dimensional ◽  
Surface Boundary ◽  
Strongly Correlated ◽  
Basin Scale ◽  
Surface Boundary Condition ◽  
Balanced Flow ◽  
Circumpolar Current ◽  
Quasigeostrophic Model

Abstract In this study, the relation between the interior and the surface dynamics for nonlinear baroclinically unstable flows is examined using the concepts of potential vorticity. First, it is demonstrated that baroclinic unstable flows present the property that the potential vorticity mesoscale and submesoscale anomalies in the ocean interior are strongly correlated to the surface density anomalies. Then, using the invertibility of potential vorticity, the dynamics are decomposed in terms of a solution forced by the three-dimensional (3D) potential vorticity and a solution forced by the surface boundary condition in density. It is found that, in the upper oceanic layers, the balanced flow induced only by potential vorticity is strongly anticorrelated with that induced only by the surface density with a dominance of the latter. The major consequence is that the 3D balanced motions can be determined from only the surface density and the characteristics of the basin-scale stratification by solving an elliptic equation. These properties allow for the possibility to reconstruct the 3D balanced velocity field of the upper layers from just the knowledge of the surface density by using a simpler model, that is, an “effective” surface quasigeostrophic model. All these results are validated through the examination of a primitive equation simulation reproducing the dynamics of the Antarctic Circumpolar Current.

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