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Nonlinear Simulations of Gravity Wave Tunneling and Breaking over Auckland Island

Tyler Mixa, Andreas Dörnbrack, and Markus Rapp

times. Gravity waves with short horizontal wavelengths are generally not included in global circulation models due to their high resolution requirements and their limited influence according to linear gravity wave theory. Linear theory for stationary mountain waves predicts a cutoff wavelength of λ x cutoff = 2 πu / N ≳ 30–50 km inside the polar night jet (PNJ) ( Schoeberl 1985 ). This cutoff suggests a widespread existence of turning levels for mountain waves with λ x ≲ 30 km in the winter

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Christopher G. Kruse and Ronald B. Smith

. Jet- or imbalance-generated gravity waves have also been studied within idealized numerical simulations ( Plougonven and Snyder 2007 ; Lin and Zhang 2008 ), which develop in synoptic-scale baroclinic systems. In these domains, synoptic-scale quasigeostrophic variations in fields (e.g., pressure) may obscure gravity wave perturbations. Realistic simulations have also been used to study real mountain wave events (e.g., Doyle et al. 2005 ; Jiang et al. 2013 ), which may also have synoptic

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

waves launched by mountainous islands near 60°S (e.g., Alexander and Grimsdell 2013 ), neglected meridional propagation or focusing of GWs into the stratospheric polar vortex jet (e.g., Sato et al. 2009 ), or underrepresented nonorographic GWs and drag resulting from jet and frontal imbalances near 60°S (e.g., Jewtoukoff et al. 2015 ) in climate simulations. It is less clear if too little planetary wave drag is part of the cold-pole problem. However, Sigmond and Scinocca (2010) found that

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

. 2002 ), STWs are highly asymmetric and often observed only on one side of the terrain. Furthermore, STWs are most commonly observed over topography located to the south of 40°S, where stratospheric winds are characterized by strong westerlies with a significant meridional shear. These wave beams seemingly emit from topography and extend southeastward toward the stratospheric jet maximum (or northeastward from terrain, located poleward of 60°S, such as the Antarctic Peninsula). While STWs have been

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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, 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

instruments. Other unique aspects included 1) extensive surveys over land and sea with long legs, 2) targeted observing to improve gravity wave predictions, and 3) better calibrated and redundant in situ airborne sensors. DEEPWAVE is also the first airborne gravity wave project over New Zealand with its isolated rugged terrain and its winter proximity to the Southern Hemisphere polar night jet allowing deep wave propagation. With these advantages, DEEPWAVE seeks new insights into atmospheric gravity wave

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Christopher G. Kruse and Ronald B. Smith

use of periodic lateral boundary conditions, 2D flow, and no planetary vorticity . These idealizations limit the ambient flow response to MWD to deceleration, preventing MWD from being balanced by a pressure gradient or Coriolis force in a barrier jet–like response. The total (nondissipative plus dissipative) MW momentum deposition and ambient flow decelerations are trivially diagnosed in the MW–ambient flow coupled WRF solutions, as the model numerics time integrate the total momentum deposition

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Ronald B. Smith and Christopher G. Kruse

Zealand comprising 97 cross-terrain legs ( Fig. 7 ). The legs were mostly flown at an altitude of in the core of the subtropical jet. These flight-level data included winds u , υ , and w , pressure p , and temperature T , so several different variance and covariance spectra can be computed. To illustrate this type of data, we show nine legs from research flight 05 (RF05) in Fig. 8 . Each trace shows the vertical parcel displacement computed from . The vertical energy fluxes were all

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