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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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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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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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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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Andreas Dörnbrack, Sonja Gisinger, Michael C. Pitts, Lamont R. Poole, and Marion Maturilli

waves are generated and propagate into the stratosphere if there is a major flow across the topography (low-level forcing), the tropospheric and stratospheric winds are large enough to avoid the formation of wave-induced critical levels, and there is no significant turning of the wind with altitude (e.g., Fritts et al. 2016 ). All these requirements were satisfied in the Svalbard region for the period from 28 to 30 December 2015. The horizontal wind in the lower troposphere (averaged from 2- to 5

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