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

1. Introduction Mountain waves under transient tropospheric forcing conditions were frequently observed during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) in austral winter 2014 ( Fritts et al. 2016 ). These events occurred episodically and were associated with migratory low pressure systems impinging the South Island (SI) of New Zealand (NZ; Gisinger et al. 2017 ). During these events, the conditions for wave excitation and propagation varied temporally. Continuous ground

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

et al. 2003 ; Hoskins and James 2014 ; De Vries et al. 2010 ; Davies 2015 ). The present study is concerned with the inverse problem of using the balanced omega equation to estimate diabatic forcing for the processes involving inertia–gravity waves (IGWs) associated with unbalanced motion and their parameterization. As gravity waves modified by Earth’s rotation ( Holton and Hakim 2013 ), the IGWs play an important role in the atmosphere by transferring momentum and energy ( Fritts and

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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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Andreas Dörnbrack

tilt of the PNJ generally found in climatological means (see Schoeberl and Newman 2015 ). Fig . 4. Horizontal wind V H (m s −1 , color shaded) and geopotential height (m, solid lines) at (a) 1, (b) 5, and (c) 10 hPa at 1200 UTC 12 Jan 2016. Fig . 5. Horizontal wind V H (m s −1 , color shaded) along the (a) 10° and (b) 50°E meridians at 1200 UTC 12 Jan 2016. The thin solid lines are isentropes in logarithmic scaling. 3. Conditions for gravity wave excitation a. Low-level forcing Low-level winds

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Victor C. Mayta and Ángel F. Adames

used winds, temperature, and specific humidity from radiosonde data at T3 (3.2°S, 60.6°W). Important supplementary products including apparent heating ( Q 1 ), apparent drying ( Q 2 ), and large-scale vertical motion ( ω ), were obtained from variational analysis ( Tang et al. 2016 ), which are available to the community at the Atmospheric Radiation Measurement (ARM) program archive ( ). Twice

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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

wave forcing over SI, typically located upstream of New Zealand. Altogether, the DEEPWAVE area of operations encompassed a region from 65° to 30°S and from 145°E to 180°. The field phase of DEEPWAVE was conducted during May–July 2014. Measurements taken on board the two research aircraft, the NSF/NCAR GV and the DLR Falcon, provided gravity wave data from the lower troposphere to the mesosphere using a variety of in situ and remote sensing instruments ( Fritts et al. 2016 ). The aircraft

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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

numerical simulation and NCEP GFS = National Centers for Environmental Prediction Global Forecast System. MOTIVATIONS. GWs, or buoyancy waves, for which the restoring force is due to negatively (positively) buoyant air for upward (downward) displacements, play major roles in atmospheric dynamics, spanning a wide range of spatial and temporal scales. Vertical and horizontal wavelengths, λ z and λ h , respectively, for vertically propagating GWs are dictated by their sources and propagation conditions

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

respective periods are characterized by strong-to-moderate tropospheric forcing, which excited mountain waves over northern Scandinavia. Forcing conditions are considered to be moderate if the component of the wind at 700 hPa perpendicular to the Scandinavian mountain ridge is smaller than 15 m s −1 , whereas strong forcing occurs if the wind component is larger than 15 m s −1 . Ambient westerly winds in the stratosphere favored the propagation of mountain waves in both cases. The gravity wave analysis

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Junhong Wei, Gergely Bölöni, and Ulrich Achatz

1. Introduction As one of the most fundamental physical modes in meteorology, gravity waves (GWs) are ubiquitous buoyancy oscillations in the atmosphere. The sources of excited gravity waves include, among others, topographic forcing ( Smith 1980 ; Menchaca and Durran 2017 ), convection ( Alexander et al. 1995 ; Lane et al. 2001 ), the jets ( Zhang 2004 ; Plougonven and Zhang 2014 ; Hien et al. 2018 ), frontal systems ( Snyder et al. 1993 ; Griffiths and Reeder 1996 ), and shear

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Tyler Mixa, Andreas Dörnbrack, and Markus Rapp

can reach the winter MLT ( Pautet et al. 2019 ), where high-frequency gravity wave responses transported the most momentum and eastward (upwind) gravity wave propagation correlated with elevated tropospheric forcing below. Given that small-scale gravity waves have been observed above the PNJ in the winter MLT, and given that several orographic and nonorographic sources have been shown to generate these scales of mesospheric gravity wave responses, it is essential to evaluate how tropospheric

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