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Ronald B. Smith, Alison D. Nugent, Christopher G. Kruse, David C. Fritts, James D. Doyle, Steven D. Eckermann, Michael J. Taylor, Andreas Dörnbrack, M. Uddstrom, William Cooper, Pavel Romashkin, Jorgen Jensen, and Stuart Beaton

current state of knowledge of gravity waves fluxes around the world is nicely reviewed by Geller at al. (2013) . They emphasize that satellites and global models are unable to resolve the short wavelength components of the gravity wave spectrum. In addition, wave parameterization schemes are oversimplified and differ from model to model. As a result, there are significant differences and uncertainties in regional wave momentum flux (MF) estimates. In the Southern Hemisphere winter, for example, the

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Christopher G. Kruse and Ronald B. Smith

state and small-scale perturbations. The third step takes pointwise products of the perturbation quantities to form quadratic diagnostic quantities (e.g., momentum flux). The last step involves low-pass spatial filtering to smooth the field and reduce noise, effectively “regionalizing” the diagnostics. These steps are described in the following subsections. Note that limited area models often make use of map projections leading to nonuniform grids on the earth. In the presented WRF simulations, the

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

, wave momentum flux was accumulated during accelerating forcing due to conservation of wave action. In contrast, the flow over higher mountains generated gravity wave breaking at lower levels. Here, the accumulated maximum of the zonal momentum flux during the high-drag state occurred shortly after the time of maximum wind. So far, no real-world case studies exist investigating a mountain-wave field excited by transient low-level forcing and propagating into the middle atmosphere. In this case study

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Ronald B. Smith and Christopher G. Kruse

-scale relief exceeds 1 km in the high mountain areas ( Korup et al. 2005 ). This roughness broadens the terrain spectrum and the associated wave spectra found in the atmosphere. The DEEPWAVE project design included longer flight legs flown repetitively over a small set of predefined flight tracks. This repetition allows multiple spectral analyses within each wave event. Typically, regionwide or project-total gravity wave spectra are broad and smooth, motivating a broad spectral approach to momentum flux

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

topography and initial/boundary conditions. These simulations are extensively validated against research aircraft, radiosonde, and satellite observations collected over New Zealand during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) field campaign during May–July 2014 ( Fritts et al. 2016 ). From these simulations, the vertical fluxes of horizontal momentum and GWD are quantified and compared with DEEPWAVE observations and parameterized quantities within NASA’s Modern-Era Retrospective

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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

reflected in the many seminal papers, reviews, and books describing these various processes. Examples of those addressing atmospheric GW topics of most relevance to DEEPWAVE science include the following: GW linear dynamics, propagation, conservation properties, and fluxes ( Hines 1960 ; Eliassen and Palm 1961 ; Bretherton 1969a , b ; Booker and Bretherton 1967 ; Gossard and Hooke 1975 ; Smith 1980 ; Nappo 2013 ); GW sources, characteristics, and responses ( Fritts 1984 ; Fritts and Alexander

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Ronald B. Smith and Christopher G. Kruse

wind direction. Drags for random terrains were analyzed by Blumen (1965) , Bretherton (1969) , Bannon and Yuhas (1990) . In parallel with these theoretical studies, surface observations of pressure drag ( Smith 1978 ) and aircraft observations of wave momentum flux (e.g., Lilly and Kennedy 1973 ; Bougeault et al. 1990 ; Smith et al. 2016 ) provided the motivation to include wave drag schemes in general circulation models (GCMs). Interactive wave drag–predicting schemes (i

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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

Aqua satellite in September 2003 and found three-dimensional gravity waves in the upper stratosphere emanating from the small subantarctic island of South Georgia. Alexander et al. (2009) inferred significant momentum flux deposition from these waves and, since global models typically treat grid cells containing small islands as ocean rather than land, they speculated that omission of gravity wave drag from small subantarctic islands might explain some or all of the stratospheric “cold pole

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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

-Interim and MLS to obtain the quasi-stationary PW1 amplitude. Note that this analysis is done by using a 10-day window shifted by 1 day to eliminate the influence of migrating waves such as tides. Vertical energy fluxes ( ) over the SI at 4- and 12-km altitude were computed from mesoscale simulations of the Weather Research and Forecasting (WRF) Model with a horizontal resolution of 6 km. The model was initialized and continuously guided by MERRA2 reanalyses. To compute the perturbations of pressure and

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

presented using observations and real-data numerical simulations. The remainder of this paper is organized as follows. Section 2 includes a brief description of the model configuration and the synoptic conditions for the two STW events. The characteristics of simulated STWs are illustrated in section 3 based on observations and numerical simulations. The vertical variation of STWs and associated momentum flux are analyzed in section 4 . The sensitivity of STWs to underlying topography and low

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