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Aditi Sheshadri, R. Alan Plumb, and Edwin P. Gerber

of Northern Hemisphere stratospheric final warming events . J. Atmos. Sci. , 64 , 2932 – 2946 , doi: 10.1175/JAS3981.1 . Black , R. X. , and B. A. McDaniel , 2007b : Interannual variability in the Southern Hemisphere circulation organized by stratospheric final warming events . J. Atmos. Sci. , 64 , 2968 – 2974 , doi: 10.1175/JAS3979.1 . Black , R. X. , B. A. McDaniel , and W. A. Robinson , 2006 : Stratosphere–troposphere coupling during spring onset . J. Climate , 19

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Chen Wei, Oliver Bühler, and Esteban G. Tabak

; therefore, the wave structure in the troposphere cannot be approximated well using upward-propagating waves alone. Conversely, solving for the wave field using the simplified approach in the presence of back-reflection at the tropopause leads to unphysical incoming internal waves in the upper atmosphere, which clearly do no satisfy the radiation condition there. The key factor is to enforce the proper radiation condition in the upper atmosphere as well as the kinematic and dynamic boundary conditions at

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Isla R. Simpson, Michael Blackburn, and Joanna D. Haigh

coordinate. Triangular truncation at wavenumber 42 is used and there are 15 levels between the surface and σ = 0.0185. Unlike some sGCMs used to investigate stratosphere–troposphere coupling, the model intentionally does not include a fully resolved stratosphere and does not exhibit a stratospheric polar vortex. The mean state is maintained by Newtonian relaxation of temperature toward a zonally symmetric equilibrium state. In the original configuration used in HBD05 and SBH09 , this relaxation

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Francesco d’Ovidio, Emily Shuckburgh, and Bernard Legras

1. Introduction It is now well established that the distribution of tracers in the upper troposphere and the lower stratosphere (UTLS) strongly depends on the transport and mixing properties of the flow. It is also well established that the dominant isentropic motion induces a chaotic type of tracer advection, giving rise to strongly inhomogeneous stirring (and thus, in the presence of diffusion, inhomogeneous mixing). 1 This segregates tracers into distinct well-mixed reservoirs separated by

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C. Schnadt Poberaj, J. Staehelin, and D. Brunner

propagate into the middle atmosphere ( Charney and Drazin 1961 ). c. Coupling to tropospheric dynamics In the troposphere, there is a rich spectrum of extratropical waves at the synoptic and planetary scale. In the SH, the absence of mountain chains locking the phase of planetary waves implies that atmospheric variability is mostly accounted for by transient (traveling) waves ( James 1994 ), and that stationary wave amplitudes are much smaller than their northern counterparts ( van Loon and Jenne 1972

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Peter Hitchcock, Theodore G. Shepherd, Masakazu Taguchi, Shigeo Yoden, and Shunsuke Noguchi

1. Introduction The lower polar stratosphere has been identified as a key region for the two-way coupling between the stratosphere and the troposphere. Circulation anomalies in the stratospheric polar vortices in both hemispheres have been shown to influence the extratropical tropospheric jets, whether they are caused by, for instance, ozone depletion in the Southern Hemisphere ( Thompson and Solomon 2002 ; Son et al. 2008 ) or sudden warmings in the Northern Hemisphere ( Baldwin and Dunkerton

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Masakazu Taguchi

) demonstrate enhanced seasonal forecast skill for the tropospheric circulation in the Northern Hemisphere following onset of SSWs. Regarding the Southern Hemisphere spring (when stratospheric variability is large), Roff et al. (2011) obtain better forecast skill in the troposphere several weeks after the initialization in a higher-vertical-resolution model than in a lower-resolution model. Comparing five seasonal forecasting models, Maycock et al. (2011) show that although the models underestimate the

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Peter Hitchcock and Peter H. Haynes

, and a result analogous to (8) holds for other nudging geometries. Within the context of experiments studying stratosphere–troposphere coupling, we are most interested in the winds induced throughout the atmosphere by stratospheric wave driving, as a result of the nonlocality of B . One central issue to be addressed in this paper is the nature of the differences between the winds induced by the stratospheric wave driving (defined by some appropriate projection operator) in the reference

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Rei Ueyama, Edwin P. Gerber, John M. Wallace, and Dargan M. W. Frierson

45°N. These parameter settings have been shown to produce realistic troposphere–stratosphere coupling ( Gerber and Polvani 2009 ) and a realistic BDC ( Gerber 2012 ). The reader is referred to these papers for a more detailed description of the model. The 6-hourly global European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim; Dee et al. 2011 ) data are analyzed for the 32-yr period from 1 January 1979 to 31 December 2010. The data are gridded at 1.5° latitude by 1

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Lantao Sun, Gang Chen, and Walter A. Robinson

zonal wind deceleration ( Black and McDaniel 2007b ), in the stratospheric wave drag and residual vertical circulation ( McLandress et al. 2010 ), and in the downward wave coupling between the stratosphere and the troposphere ( Shaw et al. 2010 ; Harnik et al. 2011 ). On interannual time scales, SFW events are observed to influence the seasonal transition of the tropospheric circulation, advancing or delaying it 1 or 2 weeks ( Black et al. 2006 ; Black and McDaniel 2007b ). These observational

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