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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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Christoph Zülicke, Erich Becker, Vivien Matthias, Dieter H. W. Peters, Hauke Schmidt, Han-Li Liu, Laura de la Torre Ramos, and Daniel M. Mitchell

) characterized the evolution of the middle-atmosphere temperatures during the extended-time-scale recovery phase as polar-night jet oscillations (PJOs) ( Kuroda and Kodera 2004 ). The diagnosis of both elevated stratopause and PJO phenomena requires a sophisticated diagnostic algorithm while a more simple approach would be an advantage. Beside a classification of the events in categories it should work on a daily basis and should also return a continuous index. The development of such a diagnostics is one

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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

, such as those that often accompany large radar and/or rocket facilities, have made especially valuable contributions to GW studies. This is because no single instrument can define all of the atmospheric properties and spatial and temporal variability needed to fully quantify the local GW field. Examples of these facilities include the Arctic Lidar Observatory for Middle Atmosphere Research in Norway (69.3°N); the Poker Flat Research Range in Alaska (65.1°N); the Bear Lake Observatory in Utah (42°N

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

the middle atmosphere. This becomes ever more important as the top of the atmospheric models is extended in the middle atmosphere, which is greatly affected by forcing and variability of the Rossby and gravity waves. The development of instruments (e.g., lidar, radar, and satellite imagery) that monitor the upper atmosphere layers improves our knowledge of wave interactions and can be helpful in upgrading the nonorographic wave drag schemes. Observations confirm that a significant part of the

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Mark Schlutow

et al. (2017) these values correspond to Reynolds numbers of Re ≈ 10...100 when the Mach number is Ma ≈ 0.1...0.01. These numbers are also supported by a review of Fritts (1984) . Taking these arguments into account, a realistic flow regime in terms of Mach, Froude, Reynolds, and Prandtl number most suitable for internal gravity waves in the middle/upper atmosphere region is then found by assuming (3a) υ r ⁡ ( 1 − κ ) p r / ρ r ≡ Ma = O ⁡ ( ε ) , (3b) υ r g L r ≡ Fr = O ⁡ ( ε 1 / 2 ) , (3c) ρ r

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

1. Introduction During the last decades, internal gravity waves have been studied intensely because of their importance for the circulation and structure of the middle atmosphere ( Fritts and Alexander 2003 ). The most energetic part of the gravity wave spectrum is excited in the troposphere, with prominent source mechanisms being the flow over topography (e.g., Smith et al. 2008 ), convection (e.g., Vadas et al. 2012 ), flow deformation, and vertical shear at upper-level fronts ( Plougonven

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

.R. thank the German Federal Ministry of Education and Research (BMBF) for partial support through the program Role of the Middle Atmosphere in Climate (ROMIC) and through Grant 01LG1220A. U.A. and J.W. thank the German Research Foundation (DFG) for partial support through the research unit Multiscale Dynamics of Gravity Waves (MS-GWaves) and through Grants AC 71/8-1, AC 71/9-1, and AC 71/10-1. REFERENCES Achatz , U. , 2005 : On the role of optimal perturbations in the instability of monochromatic

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Jannik Wilhelm, T. R. Akylas, Gergely Bölöni, Junhong Wei, Bruno Ribstein, Rupert Klein, and Ulrich Achatz

larger-scale flow (e.g., Palmer et al. 1986 ; Lott and Miller 1997 ; Scinocca and McFarlane 2000 ) and the GW impact on the generation of high cirrus clouds and polar stratospheric clouds (e.g., Joos et al. 2009 ). Even more conspicuous than in the lower atmosphere, however, are GW effects in the middle atmosphere. The general circulation in the mesosphere is basically controlled by GWs ( Lindzen 1981 ; Holton 1982 ; Garcia and Solomon 1985 ). This also seems to be of relevance to both medium

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Claudia Christine Stephan, Cornelia Strube, Daniel Klocke, Manfred Ern, Lars Hoffmann, Peter Preusse, and Hauke Schmidt

1. Introduction Atmospheric gravity waves (GWs) play a key role in defining the large-scale global circulation and thermal structure of the middle and upper atmosphere, and they are important drivers of global atmospheric variability on various time scales. They are the main driver of the mesospheric summer to winter pole-to-pole circulation ( Holton 1982 , 1983 ) and the reason for the cold summer mesopause ( Björn 1984 ). In the stratosphere, GWs affect the timing of the springtime

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Junhong Wei, Gergely Bölöni, and Ulrich Achatz

thus limit mesoscale predictability ( Zhang et al. 2007 ; Sun and Zhang 2016 ; Bierdel et al. 2018 ). The most important impact globally is because GWs can travel over large distances from their sources and transfer significant amounts of momentum and energy to high altitudes, which contributes to the forcing of the circulation and the variability of the middle atmosphere ( Holton and Lindzen 1972 ; Houghton 1978 ; Lindzen 1981 ; Dunkerton 1997 ; Richter et al. 2010 ; Limpasuvan et al. 2012

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