scholarly journals On the Sensitivity of Zonal-Index Persistence to Friction

2014 ◽  
Vol 71 (10) ◽  
pp. 3788-3800 ◽  
Author(s):  
Pablo Zurita-Gotor
Keyword(s):  
Internal Variability ◽  
Atmospheric Modeling ◽  
Spectral Structure ◽  
Layer Model ◽  
Internal Dynamics ◽  
Damping Effect ◽  
Long Time ◽  
Complex Models ◽  
The Mean ◽  
Two Layer Model

Abstract Friction is an important parameter in atmospheric modeling that may affect internal variability in a number of ways. It directly damps the annular-mode variability, but it also helps to maintain it through baroclinic feedbacks. Also, by determining the mean strength and position of the midlatitude jet, friction affects the internal dynamics that drive this variability. This work investigates the relevance of all of these factors for the sensitivity of the persistence of annular variability to changes in the zonal-mean friction using an idealized quasigeostrophic two-layer model. This model produces realistic variability, yet it is so simple that one can cleanly separate the different effects. It is found that the sensitivity of persistence to friction is dominated by the direct damping effect, while changes in the eddy momentum forcing and in the mean jet are not as important. As in more complex models, the persistence of the jet anomalies in this model decreases at all lags with increasing friction, but the long-time decorrelation decay rate of these anomalies is remarkably insensitive to friction. Although this implies that the eddy feedback must increase with friction to maintain the anomalies against the enhanced damping, it is shown that this is not due to baroclinic effects. A model that assumes that the eddy forcing does not change with friction can reproduce reasonably well the numerical results. The crucial factor that determines the model’s sensitivity to friction is the spectral structure of the eddy momentum forcing.

On the Thickness Ratio in the Quasigeostrophic Two-Layer Model of Baroclinic Instability

2013 ◽  
Vol 70 (5) ◽  
pp. 1505-1511 ◽  
Author(s):  
Noboru Nakamura ◽  
Lei Wang
Keyword(s):  
Growth Rate ◽  
Vertical Structure ◽  
Lower Layer ◽  
Baroclinic Instability ◽  
Thickness Ratio ◽  
Layer Model ◽  
Optimal Thickness ◽  
Zonal Wavenumber ◽  
The Mean ◽  
Two Layer Model

Abstract It is shown that the classical quasigeostrophic two-layer model of baroclinic instability possesses an optimal ratio of layer thicknesses that maximizes the growth rate, given the basic-state shear (thermal wind), beta, and the mean Rossby radius. This ratio is interpreted as the vertical structure of the most unstable mode. For positive shear and beta, the optimal thickness of the lower layer approaches the midheight of the model in the limit of strong criticality (shear/beta) but it is proportional to criticality in the opposite limit. For a set of parameters typical of the earth’s midlatitudes, the growth rate maximizes at a lower-layer thickness substantially less than the midheight and at a correspondingly larger zonal wavenumber. It is demonstrated that a turbulent baroclinic jet whose statistical steady state is marginally critical when run with equal layer thicknesses can remain highly supercritical when run with a nearly optimal thickness ratio.

The Relation between Baroclinic Adjustment and Turbulent Diffusion in the Two-Layer Model

2007 ◽  
Vol 64 (4) ◽  
pp. 1284-1300 ◽  
Author(s):  
Pablo Zurita-Gotor
Keyword(s):  
Turbulent Diffusion ◽  
Equilibrium States ◽  
Mean Flow ◽  
Layer Model ◽  
Local Closure ◽  
Wide Range ◽  
The Mean ◽  
Two Layer Model ◽  
Baroclinic Adjustment ◽  
Mean State

Abstract Baroclinic adjustment and turbulent diffusion are two popular paradigms used to describe the eddy–mean flow closure in the two-layer model, with very different implications for the criticality of the system. Baroclinic adjustment postulates the existence of preferred equilibrium states, while the turbulent diffusion framework predicts smooth variations of the mean state with the forcing. This study investigates the relevance of each paradigm over a wide range of the parameter space, including very strong changes in the diabatic forcing. The results confirm the weak sensitivity of the criticality against changes in the forcing noted by baroclinic adjustment studies but do not support the existence of preferred equilibrium states. The weak sensitivity of the mean state when the forcing is varied is consistent with the steepness of the diffusive closure predicted by homogeneous turbulence theories. These turbulent predictions have been tested locally against observed empirical diffusivities, extending a previous study by Pavan and Held. The results suggest that a local closure works well, even at low criticalities when the eddy momentum fluxes are important, provided that the criticality is generalized to include the effect of the meridional curvature potential vorticity (PV) gradient. When friction is weak, the development of this curvature may be important for halting the cascade and making the flow more linear. A remarkable difference from previous homogeneous results is that the empirical closure does not appear to steepen at low criticality. This may be due to the use of a generalized criticality or to the distinction between a local and domain-averaged closure.

scholarly journals Long-time behavior of a two-layer model of baroclinic quasi-geostrophic turbulence

2012 ◽  
Vol 53 (11) ◽  
pp. 115603 ◽  
Author(s):  
Aseel Farhat ◽  
R. Lee Panetta ◽  
Edriss S. Titi ◽  
Mohammed Ziane
Keyword(s):  
Time Behavior ◽  
Long Time Behavior ◽  
Layer Model ◽  
Long Time ◽  
Two Layer Model ◽  
Geostrophic Turbulence

Coherent structures of nonlinear barotropic-baroclinic interaction in unequal depth two-layer model

2021 ◽  
Vol 408 ◽  
pp. 126347
Author(s):  
Jiaqi Zhang ◽  
Ruigang Zhang ◽  
Liangui Yang ◽  
Quansheng Liu ◽  
Liguo Chen
Keyword(s):  
Coherent Structures ◽  
Layer Model ◽  
Two Layer Model

Propagation and localization of Rossby waves over random topography (two-layer model)

Wave Motion ◽  
1998 ◽  
Vol 28 (4) ◽  
pp. 333-352 ◽  
Author(s):  
V.I. Klyatskin ◽  
N.V. Gryanik ◽  
D. Gurarie
Keyword(s):  
Rossby Waves ◽  
Layer Model ◽  
Two Layer Model

Permafrost mapping by audiofrequency magnetotellurics

1978 ◽  
Vol 15 (10) ◽  
pp. 1539-1546 ◽  
Author(s):  
A. Koziar ◽  
D. W. Strangway
Keyword(s):  
Mackenzie Delta ◽  
Conductive Layer ◽  
Frequency Range ◽  
Layer Model ◽  
Resistive Layer ◽  
Asymptotic Models ◽  
Two Layer Model ◽  
Electrical Methods ◽  
Permafrost Mapping ◽  
Lateral Variations

The audiofrequency magnetotelluric (AMT) method has been used to study permafrost thickness near Tuktoyaktuk, N.W.T. in the Mackenzie Delta. In the frequency range of 10 Hz–10 kHz the permafrost behaves as a simple resistive layer over a conductive layer. This simple two-layer model can be inverted by asymptotic models to give a unique value for the thickness of the highly resistive frozen layer. In areas of simple layering, these results correlate well with drilling. In areas of sharp lateral variations in resistivity, depths tend to be underestimated. Unlike other electrical methods, AMT is not hampered by the presence of a surface melt layer in the summer if the conductivity–thickness product of this 'active layer' is less than about 0.03 mho (0.03 S).

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