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Sonja Gisinger, Andreas Dörnbrack, Vivien Matthias, James D. Doyle, Stephen D. Eckermann, Benedikt Ehard, Lars Hoffmann, Bernd Kaifler, Christopher G. Kruse, and Markus Rapp

tropospheric jet streams generate vertically propagating gravity waves in the troposphere and lower stratosphere ( Smith 1979 ; Gill 1982 ; Baines 1995 ; Fritts and Alexander 2003 ; Nappo 2012 ; Sutherland 2010 ; Plougonven and Zhang 2014 ). Through their far-field interactions, gravity waves constitute an important coupling mechanism in Earth’s atmosphere. The associated redistribution of momentum and energy controls the global middle-atmospheric circulation ( Dunkerton 1978 ; Lindzen 1981 ). To

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David C. Fritts, Ronald B. Smith, Michael J. Taylor, James D. Doyle, Stephen D. Eckermann, Andreas Dörnbrack, Markus Rapp, Bifford P. Williams, P.-Dominique Pautet, Katrina Bossert, Neal R. Criddle, Carolyn A. Reynolds, P. Alex Reinecke, Michael Uddstrom, Michael J. Revell, Richard Turner, Bernd Kaifler, Johannes S. Wagner, Tyler Mixa, Christopher G. Kruse, Alison D. Nugent, Campbell D. Watson, Sonja Gisinger, Steven M. Smith, Ruth S. Lieberman, Brian Laughman, James J. Moore, William O. Brown, Julie A. Haggerty, Alison Rockwell, Gregory J. Stossmeister, Steven F. Williams, Gonzalo Hernandez, Damian J. Murphy, Andrew R. Klekociuk, Iain M. Reid, and Jun Ma

= flight level, SI = South Island, CW = convective waves, FWs = frontal waves, SO = Southern Ocean. IOPs are shown in the context of the large-scale ECMWF horizontal winds from 0 to 80 km in Fig. 4 (top). The dominant feature is the polar night jet with a maximum wind often exceeding 100 m s −1 at ∼50–60 km that is presumably modulated in strength by PWs on time scales of ∼5–10 days. The poleward jet associated with frontal systems exhibits episodic maxima of ∼30–50 m s −1 at ∼8–12 km on similar

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Christopher G. Kruse and Ronald B. Smith

. Jet- or imbalance-generated gravity waves have also been studied within idealized numerical simulations ( Plougonven and Snyder 2007 ; Lin and Zhang 2008 ), which develop in synoptic-scale baroclinic systems. In these domains, synoptic-scale quasigeostrophic variations in fields (e.g., pressure) may obscure gravity wave perturbations. Realistic simulations have also been used to study real mountain wave events (e.g., Doyle et al. 2005 ; Jiang et al. 2013 ), which may also have synoptic

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Christopher G. Kruse, Ronald B. Smith, and Stephen D. Eckermann

waves launched by mountainous islands near 60°S (e.g., Alexander and Grimsdell 2013 ), neglected meridional propagation or focusing of GWs into the stratospheric polar vortex jet (e.g., Sato et al. 2009 ), or underrepresented nonorographic GWs and drag resulting from jet and frontal imbalances near 60°S (e.g., Jewtoukoff et al. 2015 ) in climate simulations. It is less clear if too little planetary wave drag is part of the cold-pole problem. However, Sigmond and Scinocca (2010) found that

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Stephen D. Eckermann, Jun Ma, Karl W. Hoppel, David D. Kuhl, Douglas R. Allen, James A. Doyle, Kevin C. Viner, Benjamin C. Ruston, Nancy L. Baker, Steven D. Swadley, Timothy R. Whitcomb, Carolyn A. Reynolds, Liang Xu, N. Kaifler, B. Kaifler, Iain M. Reid, Damian J. Murphy, and Peter T. Love

acquired. a. Split stratopause jet in July Figure 16 profiles monthly mean zonal winds at latitudes (20°–70°S) and longitudes (140°–190°E) in and around New Zealand during June (top row) and July (bottom row). Fig . 16. Latitude–pressure cross sections of reanalysis zonal winds (m s −1 ; see underlying color bars) averaged over months of (top) June and (bottom) July. (a),(f) MERRA2 averaged from 1998 to 2017 within a DEEPWAVE zone from 140° to 190°E; (b),(g) MERRA2 for 2014 averaged from 140° to 190°E

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Tanja C. Portele, Andreas Dörnbrack, Johannes S. Wagner, Sonja Gisinger, Benedikt Ehard, Pierre-Dominique Pautet, and Markus Rapp

-based lidar observations in the lee of New Zealand’s Alps during DEEPWAVE revealed enhanced gravity wave activity in the stratosphere and mesosphere, which lasted about 1–3 days and alternated with quiescent periods ( Kaifler et al. 2015 ). The gravity wave forcing due to passing weather systems, the appearance of tropopause jets, and the middle atmosphere wave response were all observed with a similar frequency and duration of 2–4 days ( Fritts et al. 2016 ; Gisinger et al. 2017 ). The episodic nature

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Qingfang Jiang, James D. Doyle, Stephen D. Eckermann, and Bifford P. Williams

. 2002 ), STWs are highly asymmetric and often observed only on one side of the terrain. Furthermore, STWs are most commonly observed over topography located to the south of 40°S, where stratospheric winds are characterized by strong westerlies with a significant meridional shear. These wave beams seemingly emit from topography and extend southeastward toward the stratospheric jet maximum (or northeastward from terrain, located poleward of 60°S, such as the Antarctic Peninsula). While STWs have been

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Benjamin Witschas, Stephan Rahm, Andreas Dörnbrack, Johannes Wagner, and Markus Rapp

). GWs are commonly excited in the troposphere by flow over orography (e.g., Smith et al. 2008 ; Teixeira 2014 ), convection (e.g., Vadas et al. 2012 ), or flow deformation, for instance, caused by jets and fronts ( Plougonven and Zhang 2014 ). Although there is a general understanding of processes launching GWs, the nature of wave source spectra is more complex and less well understood. For example, steady flow over topographic features will launch GWs of zero ground phase velocity ( Smith 1989

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Benedikt Ehard, Peggy Achtert, Andreas Dörnbrack, Sonja Gisinger, Jörg Gumbel, Mikhail Khaplanov, Markus Rapp, and Johannes Wagner

was often aligned with the evolving polar night jet. This flow constellation is known to excite mountain waves and to facilitate their vertical propagation into the lower and middle stratosphere (e.g., Dörnbrack et al. 2001 ). Figure 2 presents the temporal evolution of temperature and wind above Esrange for the period from 21 November to 15 December 2013. The atmospheric parameters are taken from 6-hourly operational analyses of the IFS. The vertical temperature distribution shows a cold

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Stephen D. Eckermann, Dave Broutman, Jun Ma, James D. Doyle, Pierre-Dominique Pautet, Michael J. Taylor, Katrina Bossert, Bifford P. Williams, David C. Fritts, and Ronald B. Smith

), with wind speeds increasing with height into a strong southwesterly tropospheric jet. High-resolution regional forecasts centered over Auckland Island using the U.S. Naval Research Laboratory (NRL) Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS: Hodur 1997 ; Doyle et al. 2011 ) and Mountain Wave Forecast Model ( Eckermann et al. 2006b ) predicted wave generation and penetration of orographic gravity waves into the stratosphere. Fig . 2. (a) Time evolution of horizontal wind vectors

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