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Yu Zhang
and
Joseph Pedlosky

main mechanism of decay, and the basic wave breaks down rapidly into an eddy field before it reaches the western boundary. By considering the parametric dependence of the ratio on latitude, possible only on the planetary scale, one could draw the conclusion that Z increases toward the high-latitude regions as the Coriolis parameter increases northward, which, as suggested by LaCasce and Pedlosky, is the reason for the confinement of wave patterns found in satellite measurements. This argument is

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John R. Albers
and
Thomas Birner

, our analysis will show that split and displacement SSWs indeed have very distinct prewarming evolutions. However, in contrast to Charlton and Polvani (2007) and Bancala et al. (2012) , who focused on planetary waves in the region below 30 km (10 hPa), we extend our analysis upward to 55 km (0.5 hPa) and analyze the combined effects of both planetary waves and gravity waves on vortex preconditioning and the resonant excitation theory of SSWs. In doing so, we focus particular attention on split

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Andrew J. Willmott
and
Estanislao Gavilan Pascual-Ahuir

relation for divergent barotropic planetary waves in a flat bottom polar basin. In related meteorological studies, Haurwitz (1975) and Bridger and Stevens (1980) use cylindrical polar coordinates to study freely propagating waves in a high-latitude atmosphere. The concept of the delta ( δ )-plane approximation for quasigeostrophic dynamics at high latitudes was developed by Harlander (2005) . Harlander (2005) demonstrates that the high-latitude δ -plane model can be consistently derived from

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Kevin M. Grise
and
David W. J. Thompson

climate, including the surface westerlies and the horizontal distribution of temperature. In the tropics, baroclinic instability is inhibited by weak rotation and small horizontal temperature gradients. Here, quasi-stationary equatorial planetary waves forced by the latent heat release from deep convection play a key role in the large-scale atmospheric circulation. Equatorial planetary waves are readily observed in the climatological-mean tropical circulation and are dominated by 1) an equatorially

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Randal D. Koster
,
Yehui Chang
, and
Siegfried D. Schubert

resolve key processes at all relevant scales. Here we use an AGCM to explore one particular mechanism for remote soil moisture impacts on meteorological fields, a mechanism involving the phase locking of a planetary wave over a specific soil moisture pattern. We start in section 2 with a diagnostic analysis of AGCM simulations. This analysis provides the information needed to design specialty simulations ( section 3 ) that confirm the operation of the mechanism within the model. Supporting evidence

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C. Todd Rhodes
,
Varavut Limpasuvan
, and
Yvan Orsolini

1. Introduction Occurring in ∼50% of boreal winters, an enhancement of quasi-stationary planetary waves of zonal wavenumbers 1 and 2 can result in sudden stratospheric warmings (SSWs) (e.g., Butler et al. 2015 ). Upon dissipation, these waves strongly decelerate the stratospheric flow, inducing an overturning mean meridional circulation that adiabatically warms the polar region. The anomalous polar warming causes the stratopause to descend below its climatological altitude ( Matsuno 1971

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Kaoru Sato
and
Masahiro Nomoto

possible cause of the instability is planetary wave (PW) forcing (PWF) (e.g., Baldwin and Holton 1988 ; Geer et al. 2013 ). More recently, the role of gravity wave (GW) forcing (GWF) 1 in the formation of the unstable condition is also a subject of focus (e.g., McLandress and McFarlane 1993 ; Norton and Thuburn 1996 ; Watanabe et al. 2009 ; Ern et al. 2011 ). It is well known that GWF in the upper mesosphere is important as a driving force of the residual mean circulation from the summer

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Lin Wang
,
Ronghui Huang
,
Lei Gu
,
Wen Chen
, and
Lihua Kang

EAWM was independent of the Siberian high. Since variability of the AO can significantly modulate the propagation of quasi-stationary planetary waves between the troposphere and the stratosphere ( Chen et al. 2000 , 2003 ; Chen and Huang 2005 ), Chen et al. (2005) examined the interannual AO–EAWM relationship from the perspective of the quasi-stationary planetary wave activity (PWA). They found that during the positive phase of the AO, more quasi-stationary planetary waves propagate from high

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Judith Berner
and
Grant Branstator

1. Introduction a. Background Nonlinearities in the internal dynamics of the atmosphere have the potential to influence the behavior of planetary waves in key respects. For example they can produce highly predictable states, and they can affect the way planetary waves react to external forcing ( Palmer 1999) . Although effects of nonlinearity are obvious in highly truncated models, as for example in the formation of multiple equilibria in Charney and DeVore’s (1979) model of planetary waves

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Oliver Watt-Meyer
and
Paul J. Kushner

, including a detailed comparison with previous approaches and an overview of the climatological wavenumber–frequency spectra in the extratropics. To investigate planetary wave interference effects, we will compare the structure of the standing waves and the climatological wave field. Last, we will compute the vertical and time-lagged coherences of the standing and traveling waves at selected Northern Hemisphere extratropical locations using correlation-coherence analysis ( Randel 1987 ). Section 4 will

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