scholarly journals Instability of Surface Quasigeostrophic Vortices

2009 ◽  
Vol 66 (4) ◽  
pp. 1051-1062 ◽  
Author(s):  
Xavier Carton
Keyword(s):  
Vortex Core ◽  
Temperature Anomaly ◽  
Finite Amplitude ◽  
Temperature Gradients ◽  
Barotropic Instability ◽  
Vortex Instability ◽  
Considerable Similarity ◽  
Mean Temperature ◽  
Model Evidence ◽  
2D Model

Abstract The instability of circular vortices is studied numerically in the surface quasigeostrophic (SQG) model, and their evolutions are compared with those of barotropically unstable 2D vortices. The growth rates in the SQG model evidence similarity with their barotropic counterparts for moderate radial gradients of temperature (or of vorticity in the 2D model). For stronger gradients, SQG vortices are more unstable than 2D vortices. The nonlinear, finite-amplitude evolutions of perturbed vortices provide evidence that moderately unstable, elliptically perturbed vortices form tripoles. When they are more unstable, they break into two dipoles. Weakly unstable vortices with triangular perturbations form transient quadrupoles that break; they stabilize only for large gradients of mean temperature. Finally, with square perturbations, pentapoles degenerate into dipoles, at least for the range of mean temperature gradients explored here. The analysis of nonlinear stabilizations reveals that the deformation of the vortex core and the leak of its temperature anomaly to the periphery are essential ingredients to stabilize the perturbation at finite amplitude. In conclusion, SQG vortex instability exhibits considerable similarity to the barotropic instability of 2D vortices.

scholarly journals Stratification Analysis and Behaviour of a Real Industrial Thermocline Thermal Energy Storage Tank for Cogeneration Purposes

Processes ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 120
Author(s):  
Francisco Fernández ◽  
José Díaz ◽  
María Folgueras ◽  
Inés Suárez
Keyword(s):  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Control Strategies ◽  
Storage System ◽  
Good Control ◽  
Energy Storage System ◽  
Temperature Gradients ◽  
Operation Conditions ◽  
Mean Temperature

Thermal energy storage systems help to couple thermal energy generation and process demand in cogeneration facilities. One single deposit with two design temperatures and one main temperature step in sensible thermal energy storage define the thermocline systems. Performance of one high size real thermocline thermal energy storage system is analysed. Starting from temperature and mass flow rate data registered by the plant control system, one advanced thermodynamic analysis is performed. The quality of heat storage is analysed in terms of evaluation of the stratification in the thermocline zone. The temperature data registered at 21 positions is extended by displacement analysis generating detailed profiles. Fraction of recoverable heat, thermocline width, stratification indices based on energy and exergy analysis, and mean temperature gradients in the thermocline region are calculated. These parameters are monitored under real operation conditions of the plant. The calculated parameters are studied to check their distribution and correlation. First and Second Law indices show parallel behaviour and two values are found that delimit situations of high and low values of mean temperature gradients. It was observed that buoyancy generates uniform forced movement with the right water temperature entering the diffusers, but good control strategies are essential to avoid mixing. The system demonstrated great stability in this use.

Effects of plane progressive irrotational waves on thermal boundary layers

1971 ◽  
Vol 50 (2) ◽  
pp. 321-334 ◽  
Author(s):  
James Witting
Keyword(s):  
Boundary Layers ◽  
Deep Water ◽  
Maximum Amplitude ◽  
Capillary Waves ◽  
Temperature Gradients ◽  
Two Dimensional ◽  
Inviscid Incompressible Fluid ◽  
Mean Temperature ◽  
The Waves ◽  
Thermal Boundary Layers

The average changes in the structure of thermal boundary layers at the surface of bodies of water produced by various types of surface waves are computed. the waves are two-dimensional plane progressive irrotational waves of unchanging shape. they include deep-water linear waves, deep-water capillary waves of arbitrary amplitude, stokes waves, and the deep-water gravity wave of maximum amplitude.The results indicate that capillary waves can decrease mean temperature gradients by factors of as much as 9·0, if the average heat flux at the air-water interface is independent of the presence of the waves. Irrotational gravity waves can decrease the mean temperature gradients by factors no more than 1·381.Of possible pedagogical interest is the simplicity of the heat conduction equation for two-dimensional steady irrotational flows in an inviscid incompressible fluid if the velocity potential and the stream function are taken to be the independent variables.

A Simple Mechanism for ENSO Residuals and Asymmetry

2006 ◽  
Vol 19 (13) ◽  
pp. 3167-3179 ◽  
Author(s):  
Paul S. Schopf ◽  
Robert J. Burgman
Keyword(s):  
Southern Oscillation ◽  
Finite Amplitude ◽  
Lagrangian Description ◽  
Temperature Structure ◽  
Kinematic Effect ◽  
Simple Mechanism ◽  
Surface Temperatures ◽  
Mean Temperature ◽  
Decadal Scale ◽  
Mean Sea Surface

Abstract A simple mechanism is offered that accounts for a change in the long-term (decadal scale) mean of ocean temperatures as the El Niño–Southern Oscillation (ENSO) amplitude changes. It is intended as an illustration of a kinematic effect of oscillating a nonlinear temperature profile with finite-amplitude excursions that will cause the Eulerian time mean temperature to rise (fall) where the curvature of the temperature is positive (negative) as the amplitude of the oscillations increases. This mechanism is found to be able to mimic observed changes in the mean sea surface temperatures in the Pacific between the 1920s, 1960s, and 1990s due to the changing ENSO amplitude. The effects alter both the calculated mean surface temperatures and the time mean temperatures at depth. It also results in a skewness of the temperature distribution that shares many properties with the observed SST. In this model, the time-local gradients of temperature never change if referenced to a single isotherm (i.e., the Lagrangian description is one of DT/Dt = 0). This implies that changes in the amplitude of ENSO will have no influence on the stability of the underlying system, and that the simple Eulerian decadal mean temperature structure has no predictive value. This is in direct contrast to recent work that ascribes a change in ENSO statistics as due to a change in the background state.

scholarly journals Barents Sea thermal frontal zones variability in 1960–2018

Trudy VNIRO ◽  
2020 ◽  
Vol 180 ◽  
pp. 60-71
Author(s):  
V. A. Ivshin ◽  
A. G. Trofimov ◽  
O. V. Titov
Keyword(s):  
Temperature Gradient ◽  
Interannual Variability ◽  
Barents Sea ◽  
Temperature Gradients ◽  
The Barents Sea ◽  
Mean Temperature ◽  
Frontal Zones ◽  
The 1960S ◽  
Centers Of Mass ◽  
Grid Nodes

This paper discusses our research on the interannual variability in the Barents Sea thermal frontal zones. The length index of the thermal frontal zones (the number of grid nodes with a relevant temperature gradient) and their mean temperature gradients at 50 m depth in August-September 1960–2018 were calculated for an area between 73–78°N, 15–43°E, where the frontal zones are more evident. Thermal frontal zones were identified in the areas where temperature gradients exceeded 0.04 °C/km. Since the beginning of this century, the length index of thermal frontal zones in the Barents Sea has been decreasing and temperature gradients in them have been weakening; in 2010, the length index of frontal zones and the mean temperature gradient reached record low values since 1960. To estimate interannual variability in the positions of thermal frontal zones, their geographical centroids (weighted centers of mass for grid nodes with a relevant temperature gradient) were calculated, taking into account horizontal temperature gradients as weighting coefficients. From the 1960s to the 2010s, the decadal mean centroids of frontal zones shifted northeastwards by 150 km.

Barents Sea thermal frontal zones in 1960–2017: variability, weakening, shifting

2019 ◽  
Vol 76 (Supplement_1) ◽  
pp. i3-i9
Author(s):  
Viktor A Ivshin ◽  
Alexander G Trofimov ◽  
Oleg V Titov
Keyword(s):  
Interannual Variability ◽  
Barents Sea ◽  
Temperature Gradients ◽  
The Barents Sea ◽  
Mean Temperature ◽  
Frontal Zones ◽  
The 1960S

Abstract This paper discusses our research on the interannual variability in the Barents Sea thermal frontal zones. The extent of the frontal zones and their mean temperature gradients at 50 m depth in August–September 1960–2017 were estimated for an area between 73–78°N and 15–43°E, where the frontal zones are more evident. Thermal frontal zones were identified in areas where temperature gradients exceeded 0.04°C km−1. Since the beginning of this century, the extent of the frontal zones has been decreasing and temperature gradients have been weakening. From the 1960s to the 2010s, the decadal mean centroids of thermal frontal zones shifted northeastwards by 150 km.

Wave-induced distortions of a slightly stratified shear flow: a nonlinear critical-layer effect

1973 ◽  
Vol 58 (4) ◽  
pp. 727-735 ◽  
Author(s):  
Richard Haberman
Keyword(s):  
Thermal Diffusivity ◽  
Shear Flow ◽  
Finite Amplitude ◽  
Critical Layer ◽  
Mean Temperature ◽  
Layer Effect ◽  
Stratified Shear Flow ◽  
The Mean ◽  
Wave Induced

A slightly stratified shear flow is considered when the effects of nonlinearity, viscosity and thermal diffusivity are in balance in the critical layer. Finite amplitude essentially non-diffusive neutral waves exist only if the mean temperature, velocity and vorticity profiles are distorted such that small jumps in these quantities occur across the critical layer.

Finite amplitude convection with changing mean temperature. Part 2. An experimental test of the theory

1968 ◽  
Vol 33 (3) ◽  
pp. 457-463 ◽  
Author(s):  
Ruby Krishnamurti
Keyword(s):  
Heat Flux ◽  
Fluid Layer ◽  
Vertical Direction ◽  
Finite Amplitude ◽  
Photographic Film ◽  
Static State ◽  
Mean Temperature ◽  
Constant Rate ◽  
The Mean ◽  
Rayleigh Numbers

It has been found in part 1 (Krishnamurti 1968) that when the mean temperature of a fluid layer is changing at a constant rate η, hexagonal flows are stable in a range of Rayleigh numbers near the critical. The direction of flow depends upon the sign of η. The static state is unstable to finite amplitude disturbances at Rayleigh numbers below the critical point predicted by linear theory.The validity of this theory is tested in an experiment in which the heat flux is measured as a function of η and Rayleigh number. The horizontal plan form is determined from the side by continuously exposing a photographic film moving in a vertical direction as tracers in different regions of the fluid are illuminated. Finite amplitude instability and hexagonal cells are indeed observed.

Formation of columnar baroclinic vortices in thermally stratified nonlinear spin-up

2012 ◽  
Vol 702 ◽  
pp. 265-285 ◽  
Author(s):  
J. R. Pacheco ◽  
R. Verzicco
Keyword(s):  
Vortex Core ◽  
Stokes Equations ◽  
Fluid Layer ◽  
Three Dimensional ◽  
Temperature Gradients ◽  
Navier Stokes ◽  
Central Vortex ◽  
Slip Boundary ◽  
Aspect Ratios ◽  
Vorticity Production

AbstractWe investigate the mechanisms that affect the formation of columnar vortices for spin-up in a cylinder where the temperatures at the horizontal walls are prescribed. Numerical results from the three-dimensional Navier–Stokes equations show that a short-lived instability, suppressed by the combined effect of rotation and stratification, generates small temperature variations in the azimuthal direction. Temperature-gradient anomalies produce vorticity, and these vortices stir the fluid at the interface of the central vortex core thus reinforcing the temperature gradients. For sufficiently strong temperature gradients, the central vortex core breaks up into several columnar vortices. It is found, in particular, that small aspect ratios (height over radius of the cylindrical fluid layer) $\Gamma = 1, 2$ tend to inhibit the instability, while larger ones, $\Gamma = 3. 3$, have the opposite effect. The main source of instability is the baroclinic vorticity production and not the presence of a solid sidewall since, counter-intuitively, the flow is more unstable for a free-slip boundary than for a no-slip one. Finally the effect of the temperature boundary conditions (isothermal versus adiabatic) on the horizontal boundaries has been investigated. The adiabatic boundaries help to preserve for longer times the sloping density interfaces that feed, with their potential energy, the baroclinic vorticity production; this results in more unstable flows.

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