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Christopher G. Kruse and Ronald B. Smith

exerted on the mountains by the atmosphere and momentum is transferred to Earth. An equal and opposite force is exerted by the mountain onto the lowest layers of the atmosphere, and MWs propagate this negative MF upward, depositing it wherever they dissipate. As much of Earth’s terrain and resulting MW spectra are unresolved in general circulation models and many weather prediction models, MW generation, propagation, and dissipation are parameterized. Including these parameterizations improves

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

little to nearly half of tropopause-level tropical upwelling among model members. Surprisingly, despite variable GWD contributions, the circulation strength was found to be relatively constant, implying changes in planetary wave driving compensate variations in GW forcing (e.g., Cohen et al. 2013 ) and that the mean transport circulation alone may not strongly constrain GWD parameterizations. A current common problem in chemistry–climate models is that the Southern Hemisphere pole is too cold in the

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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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Johnathan J. Metz, Dale R. Durran, and Peter N. Blossey

al. 2008 ). Three domains centered over a Lambert conformal conic projection of New Zealand were used with horizontal grid spacings of 18, 6, and 1 km, as shown in Fig. 1 . Terrain was specified using the USGS GTOPO30 dataset after filtering to minimize forcing at poorly resolved short wavelengths. The filtering was done using a nine-point approximation to the two-dimensional Laplacian operator given by (1) h ˜ i , j = h i , j + a ⁡ [ ∑ ⁡ ( ⁡ [ 1 6 2 3 1 6 2 3 − 10 3 2 3 1 6 2 3 1 6 ] ∘ ⁡ [ h 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

value problem with “switch on” of surface forcing at t = 0. Since each harmonic ( k , l ) has an associated group propagation time to reach a given height z , then imposing a fixed cutoff time limit t prop ( k , l , z c ) = t c and solving numerically for z in (7) yields a spectrum of corresponding cutoff altitudes z c ( k , l , t c ). We can use this result to approximate the time-dependent wave field solution X ( x , y , z , t ) at time t = t c using the inverse Fourier

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Ronald B. Smith and Christopher G. Kruse

1. Introduction Mountain wave drag is a horizontal pressure force acting on the terrain associated with the generation of gravity waves. The equal and opposite reaction force on the atmosphere is applied at some higher altitude where the gravity waves dissipate their energy. Since the recognition that mountain wave drag could influence the general circulation of the atmosphere ( Sawyer 1959 ; Blumen 1965 ; Bretherton 1969 ; Lilly 1972 ), there have been numerous theoretical attempts to

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Christopher G. Kruse and Ronald B. Smith

confined in frequency between the Brunt–Väisälä frequency and the Coriolis parameter: This criterion must be applied to the intrinsic frequency: the frequency seen by an air parcel as it passes through the wave. In one dimension, the intrinsic frequency may be expressed as Intrinsic frequencies higher than N cannot be caused by buoyancy forces and frequencies less than | f | are prevented by the Coriolis force. If perturbations are wavelike (i.e., nearly periodic), the intrinsic frequency can be

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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

comparable to the Coriolis force time scale of 3 h at 44°S latitude. c. Spatial filter analysis While spectral and wavelet analyses ( Figs. 11 and 13 ) are useful for leg-by-leg scale analysis, it is not possible to show such diagrams for all 97 New Zealand legs. Instead, we turn to high- and low-pass spatial filters for a statistical-scale analysis of all the New Zealand DEEPWAVE legs. Here we use a triangle (i.e., “double boxcar”) low-pass filter which attenuates the shorter waves according to where

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

nonlinear wave response, with possible flow splitting to the north and south and enhanced “high drag” MW forcing near the surface (e.g., Smith 1989 ; Eckermann et al. 2010 ). In the stratosphere, the wind speed increases from a local minimum of ~30 m s −1 at the tropopause to ~100 m s −1 at 45 km MSL. Directional wind shear is evident across the upper troposphere–lower stratosphere (UTLS; located between ~10 and 20 km). The potential temperature profile exhibits a sudden increase near 12 km, where

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