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Giuseppe Zappa
,
Valerio Lucarini
, and
Antonio Navarra

1999 ), and for detecting climate change signals as perturbations in the frequency of occurrence of the weather regimes ( Corti et al. 1999 ). The development of a self-consistent theory of the LFV is complicated by the number of different, but interacting, processes that underlie its dynamics so that simplified models have been introduced in order to cope with only a limited number of mechanisms ( Swanson 2002 ). Many of these mechanisms, such as the baroclinic–orographic resonance via form drag

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Noboru Nakamura
and
Lei Wang

1. Introduction The quasigeostrophic two-layer model, developed more than 60 yr ago by Phillips (1951) , contains all essential ingredients of large-scale dynamics in the midlatitude yet its solutions are accessible through elementary mathematics and affordable numerical integrations. Held (2005) refers to the model as the “ E. coli of climate models” (p. 1612), drawing analogy to the guiding roles played by the microorganism in molecular biology. In applications to atmospheric baroclinic

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Paul A. O’Gorman
and
Tapio Schneider

supercriticality that measures the baroclinic instability of a flow has been useful for understanding both two-layer ( Held and Larichev 1996 ) and continuously stratified ( Pedlosky 1979 ) QG models. Schneider and Walker (2006) found that a similar supercriticality based on near-surface potential temperature gradients was appropriate in characterizing the turbulence in simulated atmospheres with nonzero surface potential temperature gradients. We have already discussed in section 3 how the reversal of the

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Pablo Zurita-Gotor
and
Geoffrey K. Vallis

quasigeostrophic (QG) models. Although linear baroclinic instability theory is well established, the relevance, or even the existence, of modal development or exponential growth for the eddy–mean flow interaction problem is unclear, and the equilibration of baroclinic eddies at finite amplitude remains a complex problem. An early attempt to address the nonlinear problem was that of Green (1970) , who attempted to build a theory of the general circulation based on the diffusion of potential vorticity (PV) by

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Joseph Bernstein
and
Brian Farrell

AGCM studies. Section 5 contains the conclusions and discusses the future direction of this work. 2. Equations A two-level baroclinic potential vorticity model with relaxation to a baroclinic equilibrium velocity structure is used ( DelSole 1996 ). Our model differs from DelSole’s model in the use of meridional sponge layers to enforce radiation boundary conditions and a scale-selective diffusion. The equations for the upper- and lower-level streamfunctions ( ϕ 1 and ϕ 2 ) are written in terms

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Christopher A. Davis

vortexlike characteristics. The distinction between convective systems and baroclinic cyclones becomes blurred. Untangling this duality is central to understanding the dynamical identity of phenomena such as subtropical cyclones in which condensation processes are prominent. The present paper attempts to clarify the dynamical characteristics of subtropical cyclones through the use of an idealized baroclinic channel model with parameterized effects of condensation heating. The model is the Advanced

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Hylke de Vries

1. Introduction and model equations It has long been recognized that the continuous spectrum (CS) plays a role in the barotropic and baroclinic initial-value problem ( Orr 1907 ; Case 1960a , b ; Pedlosky 1964 ; Burger 1966 ; Farrell 1982 ). The CS has been investigated previously for geometries in which the basic-state potential vorticity (PV) gradient vanishes in the interior, such as the Eady (1949) model (e.g., Chang 1992 ; Jenkner and Ehrendorfer 2006 ; De Vries and Opsteegh 2007

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Annick Terpstra
and
Thomas Spengler

three-dimensional pressure distribution by integrating hydrostatically upward and downward, given a horizontal pressure distribution at a midtropospheric level as well as the three-dimensional temperature field ( Nuss and Anthes 1987 ; Olson and Colle 2007 ; Schemm et al. 2013 ). A variation of this approach is used by Chuang and Sousounis (2000) , who define the horizontal pressure distribution at the surface instead of the midtroposphere. To initiate development, baroclinic channel models often

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Pablo Zurita-Gotor
and
Geoffrey K. Vallis

dry model), the bulk of the dynamical forcing is nonlinear and results from the correlation between departures from the time mean. The closure problem requires relating these eddy fluxes to the mean state. This is of course a very hard problem. In fact, it could even be ill posed, as different eddy fluxes could in principle be consistent with the same mean state. Indeed, one possible closure is baroclinic adjustment ( Stone 1978 ), which assumes that the system has some preferred equilibria toward

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Pablo Zurita-Gotor
,
Javier Blanco-Fuentes
, and
Edwin P. Gerber

of this study is to test the robustness of the baroclinic feedback mechanism and to investigate the relation between barotropic and baroclinic variability more generally. This is a very challenging and largely unexplored question. Our understanding of the extratropical circulation is primarily based on two types of models: closure theories for the mean-state and initial-value (“eddy life cycle”) problems ( Zurita-Gotor and Lindzen 2007 ). Yet it is not clear that the intuition gained through

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