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Andreas Dörnbrack

. East of 30°E, the low-level winds became more southerly. The polar-front jet at 300 hPa had developed above a region of enhanced middle- and lower-tropospheric baroclinicity, the polar front as seen in Fig. 1b . This upper-level jet streak had a large along-stream extent and was nearly zonally oriented at 45°N and V H > 70 m s −1 in its core ( Fig. 2b ). During the considered period, the polar-front jet bent and advanced southward in conjunction with the deepening upper-level trough. Similar to

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Victor C. Mayta and Ángel F. Adames

component is significant at the 95% level or greater. The location of the T3 ARM site (3.2°S, 60.6°W) is indicated by a green star. On the other hand, the maximum divergence at 850 hPa is located in the east of the region of maximum convection. Similar low-level features of 2-day waves are documented in Tulich and Kiladis (2012) . Convection, as observed in Fig. 3b , promotes strong easterlies resulting in low-level jet occurrences along with the wave passage ( Fig. 3a ). This mechanism affects the

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Tyler Mixa, Andreas Dörnbrack, and Markus Rapp

times. Gravity waves with short horizontal wavelengths are generally not included in global circulation models due to their high resolution requirements and their limited influence according to linear gravity wave theory. Linear theory for stationary mountain waves predicts a cutoff wavelength of λ x cutoff = 2 πu / N ≳ 30–50 km inside the polar night jet (PNJ) ( Schoeberl 1985 ). This cutoff suggests a widespread existence of turning levels for mountain waves with λ x ≲ 30 km in the winter

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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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Mahnoosh Haghighatnasab, Mohammad Mirzaei, Ali R. Mohebalhojeh, Christoph Zülicke, and Riwal Plougonven

Alexander 2003 ) over long distances and interacting with other phenomena through, for example, triggering convection. Previous observational and numerical studies have shown several sources for IGWs as orography, convection, shear instability, jet streams, and fronts (e.g., Uccellini and Koch 1987 ; Eckermann and Vincent 1993 ; O’Sullivan and Dunkerton 1995 ; Guest et al. 2000 ; Plougonven and Snyder 2007 ). The IGWs affect the atmospheric general circulation through breaking and dissipation by

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Mohammad Mirzaei, Ali R. Mohebalhojeh, Christoph Zülicke, and Riwal Plougonven

wave polarization relations. Previously, the HDA has been applied by Zülicke and Peters (2008) and Mirzaei et al. (2014) for the validation of a bulk parameterization of IGWs generated by jets, fronts, and convection. As its name suggests, the HDA’s working rests on certain assumptions on the wave field like the presence of a locally dominant wavenumber and sufficient separation with the large-scale balanced flow. By construction, the HDA performs well in regions of space filled by the coherent

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Martina Bramberger, Andreas Dörnbrack, Henrike Wilms, Steffen Gemsa, Kevin Raynor, and Robert Sharman

-air turbulence (CAT). Well-known generation processes of turbulence affecting aircraft at cruising altitudes comprise thunderstorms, strong wind shears related to upper-level fronts and jet streams, unbalanced flow, and breaking mountain waves (e.g., Vinnichenko et al. 1980 ; Lester 1993 ; Wolff and Sharman 2008 ; Lane et al. 2012 ; Sharman et al. 2012b ). Considering the generation process, turbulence directly related to breaking mountain waves is referred to as mountain wave turbulence (MWT) ( Sharman

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Gergely Bölöni, Bruno Ribstein, Jewgenija Muraschko, Christine Sgoff, Junhong Wei, and Ulrich Achatz

resulting in a constant buoyancy frequency . This implies a reference density profile where is the density scale height. Some of the test cases involve a prescribed background jet as an initial mean flow with a half-cosine wave shape: where is the maximal magnitude of the jet initialized at height , and is the width (i.e., vertical extent) of the half-cosine shape. In these cases, the wave-induced mean flow is diagnosed as : that is, the initial mean wind is subtracted from the total mean wind

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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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