Chapter 2 Theories of Baroclinic Adjustment and Eddy Equilibration

2008 ◽  
pp. 22-46
Author(s):  
Pablo Zurita-Gotor ◽  
Richard S. Lindzen
Keyword(s):  
Baroclinic Adjustment

scholarly journals Nonlinear Baroclinic Equilibration in the Presence of Ekman Friction

2012 ◽  
Vol 42 (2) ◽  
pp. 225-242 ◽  
Author(s):  
B. T. Willcocks ◽  
J. G. Esler
Keyword(s):  
Life Cycle ◽  
High Resolution ◽  
Numerical Simulations ◽  
Stability Criterion ◽  
Wave Amplitude ◽  
Ekman Number ◽  
Baroclinic Waves ◽  
Long Time ◽  
Baroclinic Adjustment ◽  
Degree Of Instability

Abstract Two theories for the nonlinear equilibration of baroclinic waves in a two-layer fluid in a β channel are tested by comparison with high-resolution numerical simulations. Predictions are tested for a range of parameters (β, κ), where the inverse criticality β measures the degree of instability and the quasigeostrophic Ekman number κ measures the strength of Ekman friction. The first theory, from Warn, Gauthier, and Pedlosky (WGP), is formally valid for marginally unstable waves at κ = 0. The second, from Romea, is formally valid for nonzero κ and for waves that are marginally stable with respect to a different criterion, which enters because of the dissipative destabilization of otherwise stable waves by Ekman friction. The predictions of the two theories are in conflict in the limit κ → 0. When κ is slightly greater than zero, it is found that the WGP accurately predicts the maximum wave amplitude attained during a baroclinic life cycle across a significant range of parameter space. By contrast, accurate predictions of the long-time asymptotic wave amplitude are obtained only from Romea’s theory, even for those cases where WGP describes the initial behavior during the life cycle accurately. The results first indicate the importance of understanding the nonlinear equilibration mechanism of dissipatively destabilized waves. Second, it follows that baroclinic adjustment theories formulated from inviscid and frictionless stability criterion make demonstrably incorrect predictions for the equilibrated state, even in the limit of vanishing Ekman friction.

Theories of Baroclinic Adjustment and Eddy Equilibration

2021 ◽  
pp. 22-46
Author(s):  
Pablo Zurita-Gotor ◽  
Richard S. Lindzen
Keyword(s):  
Baroclinic Adjustment

Importance of Diurnal Forcing on the Summer Salinity Variability in the East China Sea

2020 ◽  
Vol 50 (3) ◽  
pp. 633-653
Author(s):  
Yang Yu ◽  
Shu-Hua Chen ◽  
Yu-Heng Tseng ◽  
Xinyu Guo ◽  
Jie Shi ◽  
...  
Keyword(s):  
Yangtze River ◽  
River Estuary ◽  
Sea Breeze ◽  
Yangtze River Estuary ◽  
The Yangtze River ◽  
The East China Sea ◽  
Salinity Change ◽  
The Yangtze River Estuary ◽  
Dipole Pattern ◽  
Baroclinic Adjustment

AbstractThe impacts of diurnal atmospheric forcing on the summer salinity change in the East China Sea are investigated using the Regional Ocean Modeling System, forced by the hourly and daily reanalysis of wind and insolation. The differences between the forcing of these two frequencies reveal a dipole pattern of salinity change with a positive salinity deviation (1–2 psu) offshore of the Yangtze River estuary, and a negative deviation (from −1 to −0.5 psu) along the Jiangsu Coast. Further dye tracking experiments confirm that diurnal forcing strengthened the northwestward longshore freshwater transport (NLFT) of the Yangtze River by 5.2 × 109 m3 and reduced the mean water age of 7 days. Sensitivity experiments using different forcing combinations suggest that the diurnal wind, that is, the land–sea breeze, is the key to developing the dipole pattern of salinity change and the NLFT. Through the experiment, the land–sea breeze induced a mean clockwise circulation offshore of the Yangtze River estuary. The above changes resulted from both the nonlinearity of wind stress averaging (i.e., the square nature of wind stress) and the baroclinic adjustment related to the diurnal salinity variation, which is directly connected to the diurnal swing of the Yangtze River front. The baroclinic adjustment generated a dipole pattern of vorticity changes offshore of the Yangtze River estuary and a coherent northwestward jet current strengthening the NLFT. These processes developed the summer dipole pattern of the salinity change.

scholarly journals Baroclinic Adjustment in an Atmosphere–Ocean Thermally Coupled Model: The Role of the Boundary Layer Processes

2011 ◽  
Vol 68 (11) ◽  
pp. 2710-2730 ◽  
Author(s):  
Yang Zhang ◽  
Peter H. Stone
Keyword(s):  
Boundary Layer ◽  
Surface Energy ◽  
Sensible Heat Flux ◽  
Coupled Model ◽  
Coupled System ◽  
Surface Energy Budget ◽  
Strong Mixing ◽  
Boundary Layer Processes ◽  
Strong Surface ◽  
Baroclinic Adjustment

Abstract Baroclinic eddy equilibration and the roles of different boundary layer processes in limiting the baroclinic adjustment are studied using an atmosphere–ocean thermally coupled model. Boundary layer processes not only affect the dynamical constraint of the midlatitude baroclinic eddy equilibration but also are important components in the underlying surface energy budget. The authors' study shows that baroclinic eddies, with the strong mixing of the surface air temperature, compete against the fast boundary layer thermal damping and enhance the meridional variation of surface sensible heat flux, acting to reduce the meridional gradient of the surface temperature. Nevertheless, the requirement of the surface energy balance indicates that strong surface baroclinicity is always maintained in response to the meridionally varying solar radiation. With the strong surface baroclinicity and the boundary layer processes, the homogenized potential vorticity (PV) suggested in the baroclinic adjustment are never observed near the surface or in the boundary layer. Although different boundary layer processes affect baroclinic eddy equilibration differently with more dynamical feedbacks and time scales included in the coupled system, their influence in limiting the PV homogenization is more uniform compared with the previous uncoupled runs. The boundary layer PV structure is more determined by the strength of the boundary layer damping than the surface baroclinicity. Stronger boundary layer processes always prevent the lower-level PV homogenization more efficiently. Above the boundary layer, a relatively robust PV structure with homogenized PV around 600–800 hPa is obtained in all of the simulations. The detailed mechanisms through which different boundary layer processes affect the equilibration of the coupled system are discussed in this study.

scholarly journals Baroclinic Adjustment and Dissipative Control of Storm Tracks

2018 ◽  
Vol 75 (9) ◽  
pp. 2955-2970 ◽  
Author(s):  
Lenka Novak ◽  
Maarten H. P. Ambaum ◽  
Ben J. Harvey
Keyword(s):  
Steady State ◽  
General Circulation ◽  
Large Scale ◽  
Thermal Structure ◽  
Storm Track ◽  
Circulation Model ◽  
Thermal Forcing ◽  
Dissipative Control ◽  
Additional Support ◽  
Baroclinic Adjustment

Abstract The steady-state response of a midlatitude storm track to large-scale extratropical thermal forcing and eddy friction is investigated in a dry general circulation model with a zonally symmetric forcing. A two-way equilibration is found between the relative responses of the mean baroclinicity and baroclinic eddy intensity, whereby mean baroclinicity responds more strongly to eddy friction whereas eddy intensity responds more strongly to the thermal forcing of baroclinicity. These seemingly counterintuitive responses are reconciled using the steady state of a predator–prey relationship between baroclinicity and eddy intensity. This relationship provides additional support for the well-studied mechanism of baroclinic adjustment in Earth’s atmosphere, as well as providing a new mechanism whereby eddy dissipation controls the large-scale thermal structure of a baroclinically unstable atmosphere. It is argued that these two mechanisms of baroclinic adjustment and dissipative control should be used in tandem when considering storm-track equilibration.

Baroclinic Multiple Zonal Jets on the Sphere

2005 ◽  
Vol 62 (7) ◽  
pp. 2484-2498 ◽  
Author(s):  
Sukyoung Lee
Keyword(s):  
Temperature Difference ◽  
Potential Temperature ◽  
Plane Channel ◽  
Equation Model ◽  
Scaling Analysis ◽  
Flux Divergence ◽  
Zonal Jets ◽  
Eddy Heat Flux ◽  
Quasigeostrophic Model ◽  
Baroclinic Adjustment

Abstract Multiple zonal jets are investigated with a two-level primitive equation model on the sphere in which both baroclinicity and planetary radius are varied. As in the case for a two-layer quasigeostrophic model on a β-plane channel, it is found both that the Rhines scale successfully predicts the meridional scale of the multiple zonal jets, and that these jets are maintained in part by an eddy momentum flux divergence associated with slow baroclinic waves at the interjet minimum. A scaling analysis suggests that njets∝ (a/θm)1/2, with the constraints ζe ≡ 8 sin2f (θm/▵θ ) > 1 and njets ≥ 1, where njets is the number of the jets, a the planetary radius, θm one-half of the pole-to-equator potential temperature difference, ξe the supercriticality of the two-layer Phillips model, Δθ the potential temperature difference between the two levels, and ϕ the latitude. The number of jets simulated by the model agrees with this scaling, provided that Ljet ≤ a, where Ljet is the jet scale. In model runs with a large planet where multiple zonal jets exist, the time–mean eddy heat flux is found to be consistent with the diffusive picture of Held and Larichev. In contrast, for the model runs with the planetary size equal to that of Earth, baroclinic adjustment is found to be more relevant. These results are consistent with the finding that in the large-planet (Earth-like) model runs, the jet/eddy scale is smaller than (comparable to) the corresponding planetary radius.

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