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Christopher G. Kruse and Ronald B. Smith

-scale variations. A major objective here is to construct a method to isolate gravity wave perturbations from these synoptic-scale variations in realistic mesoscale fields. The simplest way to define gravity wave perturbation fields in realistic output is to subtract the mean (e.g., Doyle et al. 2005 ). This method may be appropriate for small domains, but gravity wave perturbations become increasingly dominated by synoptic-scale variations as domain size increases. A more sophisticated approach is to apply a

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Ronald B. Smith and Christopher G. Kruse

. Kim and Arakawa (1995) and Kim and Doyle (2005) took a new approach using numerical mesoscale models over a variety of hill shapes to derive wave drag laws. Anisotropy was treated by using a range of wind directions over specified hill shapes. In the gravity wave “parameterization” literature, the authors worked not only to predict the gravity wave drag but also to predict how the associated momentum flux would be applied to the atmosphere above the rough terrain (e.g., Shutts and Gadian 1999

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

; Doyle et al. 2011 ) were applied to the DEEPWAVE study area to provide real-time forecast guidance during the field campaign period ( Fritts et al. 2016 ). COAMPS is a fully compressible, nonhydrostatic terrain-following mesoscale model. The finite-difference schemes are of second-order accuracy in time and space in this application. The boundary layer and free-atmospheric turbulent mixing and diffusion are represented using a prognostic equation for the turbulence kinetic energy budget following

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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

), with wind speeds increasing with height into a strong southwesterly tropospheric jet. High-resolution regional forecasts centered over Auckland Island using the U.S. Naval Research Laboratory (NRL) Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS: Hodur 1997 ; Doyle et al. 2011 ) and Mountain Wave Forecast Model ( Eckermann et al. 2006b ) predicted wave generation and penetration of orographic gravity waves into the stratosphere. Fig . 2. (a) Time evolution of horizontal wind vectors

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Ronald B. Smith and Christopher G. Kruse

, quasi-two-dimensional turbulence, and vortical modes . J. Geophys. Res. , 104 , 16 297 – 16 308 , doi: 10.1029/1999JD900068 . 10.1029/1999JD900068 Durran , D. R. , 1986 : Mountain waves. Mesoscale Meteorology and Forecasting , P. Ray, Ed., Amer. Meteor. Soc., 472–492. 10.1007/978-1-935704-20-1_20 Eliassen , A. , and E. Palm , 1960 : On the transfer of energy in stationary mountain waves . Geofys. Publ. , 22 , ( 3 ), 1 – 23 . Ern , M. , P. Preusse , M. J. Alexander , and C. D

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

increasing orographic GWD significantly reduces the strength of the stratospheric polar vortex primarily by altering planetary Rossby wave propagation and drag. This result suggests that increasing parameterized orographic GWD in chemistry–climate models might reduce the cold-pole problem in free-running climate simulations. In this paper, the vertical propagation and attenuation of New Zealand mountain waves are studied using deep Weather Research and Forecasting (WRF) Model simulations with realistic

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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

expressions, the symbols g , C p , θ , Ω, and ϕ are gravity, specific heat capacity, potential temperature, Earth rotation rate, and latitude, respectively. Gravity waves play a significant role in atmospheric dynamics by dispersing mesoscale horizontal potential temperature gradients, aiding geostrophic adjustment, and transporting energy and momentum from source to sink regions ( Eliassen and Palm 1960 ; Bretherton 1969 ; Holton 1982 ; Fritts and Nastrom 1992 ; Alexander et al. 2010 ). The

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Nonlinear Simulations of Gravity Wave Tunneling and Breaking over Auckland Island

Tyler Mixa, Andreas Dörnbrack, and Markus Rapp

winter MLT. The continued absence of this MLT GWD source in global and mesoscale climate modeling suggests that addressing gravity wave tunneling dynamics is a viable approach to improve the accuracy of climate modeling in the Southern Hemisphere. Acknowledgments This research was conducted within the scope of the German research initiative Role of the Middle Atmosphere in Climate (ROMIC) under Grant 01LG1206A by the German Ministry for Education and Research. Funding was also provided by the German

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Christopher G. Kruse and Ronald B. Smith

and Doyle 2005 ; Smith and Kruse 2018 ) rather than on wave propagation, dissipation, and momentum deposition. Transient, broad-spectrum MW events are studied here using three numerical models: the fully nonlinear, transient Weather Research and Forecasting (WRF) Model ( Skamarock et al. 2008 ); the linear, quasi-transient Fourier-ray (FR) model ( Broutman et al. 2002 , 2006 ); and a Lindzen-type saturation parameterization (LSP; Lindzen 1981 ; McFarlane 1987 ) model. Key idealizations are the

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