scholarly journals Clarification on the generation of absolute and potential vorticity in mesoscale convective vortices

2009 ◽  
Vol 9 (19) ◽  
pp. 7591-7605 ◽  
Author(s):  
R. J. Conzemius ◽  
M. T. Montgomery
Keyword(s):  
Potential Vorticity ◽  
Diabatic Heating ◽  
Coriolis Parameter ◽  
Mesoscale Convective ◽  
Vorticity Generation ◽  
Heating Profiles ◽  
Convective Vortices

Abstract. In this paper, we clarify several outstanding issues concerning the predominant mechanism of vorticity generation in mesoscale convective vortices (MCVs) in weak to modest baroclinic environments with nonzero Coriolis parameter. We examine also the corresponding diabatic heating profiles of the convective and stratiform components of the MCS and their effects on the concentration and dilution of PV substance.

scholarly journals Clarification on the generation of absolute and potential vorticity in mesoscale convective vortices

2009 ◽  
Vol 9 (2) ◽  
pp. 7531-7554 ◽  
Author(s):  
R. J. Conzemius ◽  
M. T. Montgomery
Keyword(s):  
Potential Vorticity ◽  
Diabatic Heating ◽  
Dominant Role ◽  
Convective Precipitation ◽  
Absolute Vorticity ◽  
Vertical Vorticity ◽  
Stratiform Precipitation ◽  
Mesoscale Convective ◽  
Pv Generation ◽  
Convective Vortices

Abstract. The purpose of this paper is to clarify what we think are several outstanding issues concerning the predominant mechanism of vorticity generation in mesoscale convective vortices (MCVs). Using idealized mesoscale numerical simulations of MCV development, we examine here the vertical vorticity budgets in order to quantify the contributions of flux convergence of absolute vorticity versus tilting in the generation of MCV vorticity. In addition, we examine the corresponding diabatic heating profiles. By partitioning the diabatic heating between convective and stratiform regions, we elucidate the respective roles of convective and stratiform precipitation in the generation of potential vorticity (PV). The analyses indicate that the horizontal flux convergence of vertical vorticity is the dominant mechanism for the spin-up and intensification of mid-level absolute vorticity. Indeed, diabatic heating and circulation budgets demonstrate that the vertical gradient of diabatic heating is supportive of low- to mid-level PV generation. During the early stages of MCV development, convective precipitation plays the dominant role in the PV generation; later on, the stratiform precipitation expands and becomes a larger contributor, particularly in low-CAPE background environments.

scholarly journals Diagnostic study of diabatic heating and potential vorticity during a case of cyclogenesis

MAUSAM ◽  
2021 ◽  
Vol 71 (2) ◽  
pp. 255-274
Author(s):  
AL-MUTAIRI M K ◽  
BASSET H ABDEL
Keyword(s):  
Potential Vorticity ◽  
Diabatic Heating ◽  
Diagnostic Study ◽  
Transport Pathways ◽  
Low Level ◽  
Vorticity Generation ◽  
Adiabatic Term ◽  
Vorticity Anomaly ◽  
Strong Upward Motion ◽  
Maximum Development

On 16-17 November, 2015, north and middle regions of Saudi Arabia were hit by a case of cyclogenesisassociated with heavy rainfall. This work presents a diagnostic study of this heavy rainfallcase based on the analysis of diabatic heating and potential vorticity. The synoptic analysis investigate that the important dynamical factors that causes this case are the northward extension of Red Sea Trough, anticyclone over the Arabian Peninsula, a travailing midlatitude upper trough, moisture transport pathways and strong upward motion arising from tropospheric instability. The calculation of diabatic heating by the thermodynamic equation illustrate that the contribution of vertical temperature advection and the adiabatic term are opposite to each other during the period of study. The largest contribution of the horizontal cold advection occurs during the first two days while the largest contribution of the horizontal warm advection occurs during the maximum development days. The dynamics of the studied case are also investigated in terms of isobaric Potential Vorticity. It is found that the location of the low-level Potential Vorticity anomaly and the Potential Vorticity generation estimates coincides with the heating region, which implies that condensation supports a large enough source to explain the existence of the low-level Potential Vorticity anomaly.

scholarly journals Multi-symplectic formulation of near-local Hamiltonian balanced models

2011 ◽  
Vol 467 (2136) ◽  
pp. 3424-3442 ◽  
Author(s):  
Sylvain Delahaies ◽  
Peter E. Hydon
Keyword(s):  
Potential Vorticity ◽  
Contact Structure ◽  
Fluid Motion ◽  
Local Model ◽  
Contact Transformation ◽  
Geometric Features ◽  
Coriolis Parameter ◽  
New Class

We transform near-local Hamiltonian balanced models (HBMs) describing nearly geostrophic fluid motion (with constant Coriolis parameter) into multi-symplectic (MS) systems. This allows us to determine conservation of Lagrangian momentum, energy and potential vorticity for Salmon's L 1 dynamics; a similar approach works for other near-local balanced models (such as the -model). The MS approach also enables us to determine a class of systems that have a contact structure similar to that of the semigeostrophic model. The contact structure yields a contact transformation that makes the problem of front formation tractable. The new class includes the first local model with a variable Coriolis parameter that preserves all of the most useful geometric features of the semigeostrophic model.

scholarly journals Surface signature of Mediterranean water eddies in the Northeastern Atlantic: effect of the upper ocean stratification

Ocean Science ◽  
2012 ◽  
Vol 8 (6) ◽  
pp. 931-943 ◽  
Author(s):  
I. Bashmachnikov ◽  
X. Carton
Keyword(s):  
Potential Vorticity ◽  
Initial Period ◽  
Relative Vorticity ◽  
Sea Surface ◽  
Upper Ocean ◽  
Buoyancy Frequency ◽  
Coriolis Parameter ◽  
Ocean Stratification ◽  
Surface Signature ◽  
Mediterranean Water

Abstract. Meddies, intra-thermocline eddies of Mediterranean water, can often be detected at the sea surface as positive sea-level anomalies. Here we study the surface signature of several meddies tracked with RAFOS floats and AVISO altimetry. While pushing its way through the water column, a meddy raises isopycnals above. As a consequence of potential vorticity conservation, negative relative vorticity is generated in the upper layer. During the initial period of meddy acceleration after meddy formation or after a stagnation stage, a cyclonic signal is also generated at the sea-surface, but mostly the anticyclonic surface signal follows the meddy. Based on geostrophy and potential vorticity balance, we present theoretical estimates of the intensity of the surface signature. It appears to be proportional to the meddy core radius and to the Coriolis parameter, and inversely proportional to the core depth and buoyancy frequency. This indicates that surface signature of a meddy may be strongly reduced by the upper ocean stratification. Using climatic distribution of the stratification intensity, we claim that the southernmost limit for detection in altimetry of small meddies (with radii on the order of 10–15 km) should lie in the subtropics (35–45° N), while large meddies (with radii of 25–30 km) could be detected as far south as the northern tropics (25–35° N). Those results agree with observations.

scholarly journals Destruction of Potential Vorticity by Winds

2005 ◽  
Vol 35 (12) ◽  
pp. 2457-2466 ◽  
Author(s):  
Leif N. Thomas
Keyword(s):  
Boundary Layer ◽  
Wind Stress ◽  
Potential Vorticity ◽  
Ekman Layer ◽  
Buoyancy Flux ◽  
Coriolis Parameter ◽  
Mode Water ◽  
Ocean Fronts ◽  
Secondary Circulations ◽  
Frictional Forces

Abstract The destruction of potential vorticity (PV) at ocean fronts by wind stress–driven frictional forces is examined using PV flux formalism and numerical simulations. When a front is forced by “downfront” winds, that is, winds blowing in the direction of the frontal jet, a nonadvective frictional PV flux that is upward at the sea surface is induced. The flux extracts PV out of the ocean, leading to the formation of a boundary layer thicker than the Ekman layer, with nearly zero PV and nonzero stratification. The PV reduction is not only active in the Ekman layer but is transmitted through the boundary layer via secondary circulations that exchange low PV from the Ekman layer with high PV from the pycnocline. Extraction of PV from the pycnocline by the secondary circulations results in an upward advective PV flux at the base of the boundary layer that scales with the surface, nonadvective, frictional PV flux and that leads to the deepening of the layer. At fronts forced by both downfront winds and a destabilizing atmospheric buoyancy flux FBatm, the critical parameter that determines whether the wind or the buoyancy flux is the dominant cause for PV destruction is (H/δe)(FBwind/FBatm), where H and δe are the mixed layer and Ekman layer depths, FBwind = S2τo/(ρof ), S2 is the magnitude of the lateral buoyancy gradient of the front, τo is the downfront component of the wind stress, ρo is a reference density, and f is the Coriolis parameter. When this parameter is greater than 1, PV destruction by winds dominates and may play an important role in the formation of mode water.

scholarly journals On the stability of ocean overflows

2008 ◽  
Vol 602 ◽  
pp. 241-266 ◽  
Author(s):  
LARRY J. PRATT ◽  
KARL R. HELFRICH ◽  
DAVID LEEN
Keyword(s):  
Potential Vorticity ◽  
Growth Rates ◽  
Deep Ocean ◽  
Basic Flow ◽  
Necessary Condition ◽  
Zero Energy ◽  
Coriolis Parameter ◽  
Hydraulic Behaviour ◽  
Zero Potential ◽  
The Stability

The stability of a hydraulically driven sill flow in a rotating channel with smoothly varying cross-section is considered. The smooth topography forces the thickness of the moving layer to vanish at its two edges. The basic flow is assumed to have zero potential vorticity, as is the case in elementary models of the hydraulic behaviour of deep ocean straits. Such flows are found to always satisfy Ripa's necessary condition for instability. Direct calculation of the linear growth rates and numerical simulation of finite-amplitude behaviour suggests that the flows are, in fact, always unstable. The growth rates and nonlinear evolution depend largely on the dimensionless channel curvature κ=2αg′/f2, where 2α is the dimensional curvature, g′ is the reduced gravity, and f is the Coriolis parameter. Very small positive (or negative) values of κ correspond to dynamically wide channels and are associated with strong instability and the breakup of the basic flow into a train of eddies. For moderate or large values of κ, the instability widens the flow and increases its potential vorticity but does not destroy its character as a coherent stream. Ripa's condition for stability suggests a theory for the final width and potential vorticity that works moderately well. The observed and predicted growth in these quantities are minimal for κ≥1, suggesting that the zero-potential-vorticity approximation holds when the channel is narrower than a Rossby radius based on the initial maximum depth. The instability results from a resonant interaction between two waves trapped on opposite edges of the stream. Interactions can occur between two Kelvin-like frontal waves, between two inertia–gravity waves, or between one wave of each type. The growing disturbance has zero energy and extracts zero energy from the mean. At the same time, there is an overall conversion of kinetic energy to potential energy for κ>0, with the reverse occurring for κ<0. When it acts on a hydraulically controlled basic state, the instability tends to eliminate the band of counterflow that is predicted by hydraulic theory and that confounds hydraulic-based estimates of volume fluxes in the field. Eddy generation downstream of the controlling sill occurs if the downstream value of κ is sufficiently small.

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.

Barotropic flow over finite isolated topography: steady solutions on the beta-plane and the initial value problem

1993 ◽  
Vol 250 ◽  
pp. 553-586 ◽  
Author(s):  
Luanne Thompson ◽  
Glenn R. Flierl
Keyword(s):  
Rossby Wave ◽  
Potential Vorticity ◽  
Initial Value Problem ◽  
Wave Drag ◽  
Combined Effects ◽  
Initial Value ◽  
Coriolis Parameter ◽  
Finite Height ◽  
Barotropic Flow ◽  
Steady Solutions

Solutions for inviscid rotating flow over a right circular cylinder of finite height are studied, and comparisons are made to quasi-geostrophic solutions. To study the combined effects of finite topography and the variation of the Coriolis parameter with latitude a steady inviscid model is used. The analytical solution consists of one part which is similar to the quasi-geostrophic solution that is driven by the potential vorticity anomaly over the topography, and another, similar to the solution of potential flow around a cylinder, that is driven by the matching conditions on the edge of the topography. When the characteristic Rossby wave speed is much larger than the background flow velocity, the transport over the topography is enhanced as the streamlines follow lines of constant background potential vorticity. For eastward flow, the Rossby wave drag can be very much larger than that predicted by quasi-geostrophic theory. The combined effects of finite height topography and time-dependence are studied in the inviscid initial value problem on the f-plane using the method of contour dynamics. The method is modified to handle finite topography. When the topography takes up most of the layer depth, a stable oscillation exists with all of the fluid which originates over the topography rotating around the topography. When the Rossby number is order one, a steady trapped vortex solution similar to the one described by Johnson (1978) may be reached.

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.

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