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Andreas Dörnbrack


Planetary waves disturbed the hitherto stable Arctic stratospheric polar vortex in the middle of January 2016 in such a way that unique tropospheric and stratospheric flow conditions for vertically and horizontally propagating mountain waves developed. Co-existing strong low-level westerly winds across almost all European mountain ranges plus the almost zonally-aligned polar front jet created these favorable conditions for deeply propagating gravity waves. Furthermore, the northward displacement of the polar night jet resulted in a wide-spread coverage of stratospheric mountainwaves trailing across northern Europe. This paper describes the particular meteorological setting by analyzing the tropospheric and stratospheric flows based on the ERA5 data. The potential of the flow for exciting internal gravity waves from non-orographic sources is evaluated across all altitudes by considering various indices to indicate flow imbalances as δ, Ro, Roζ, Ro, and ΔNBE. The analyzed gravity waves are described and characterized. The main finding of this case study is the exceptionally vast extension of the mountain waves trailing to high latitudes originating from the flow across the mountainous sources that are located at about 45°N. The magnitudes of the simulated stratospheric temperature perturbations attain values larger than 10K and are comparable to values as documented by recent case studies of large-amplitude mountain waves over South America. The zonal means of the resolved and parameterized stratospheric wave drag during the mountain wave event peak at − 4.5ms−1 d−1 and − 32.2 ms−1 d−1, respectively.

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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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Mahnoosh Haghighatnasab, Mohammad Mirzaei, Ali R. Mohebalhojeh, Christoph Zülicke, and Riwal Plougonven

Alexander 2003 ) over long distances and interacting with other phenomena through, for example, triggering convection. Previous observational and numerical studies have shown several sources for IGWs as orography, convection, shear instability, jet streams, and fronts (e.g., Uccellini and Koch 1987 ; Eckermann and Vincent 1993 ; O’Sullivan and Dunkerton 1995 ; Guest et al. 2000 ; Plougonven and Snyder 2007 ). The IGWs affect the atmospheric general circulation through breaking and dissipation by

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Mohammad Mirzaei, Ali R. Mohebalhojeh, Christoph Zülicke, and Riwal Plougonven

wave polarization relations. Previously, the HDA has been applied by Zülicke and Peters (2008) and Mirzaei et al. (2014) for the validation of a bulk parameterization of IGWs generated by jets, fronts, and convection. As its name suggests, the HDA’s working rests on certain assumptions on the wave field like the presence of a locally dominant wavenumber and sufficient separation with the large-scale balanced flow. By construction, the HDA performs well in regions of space filled by the coherent

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Gergely Bölöni, Bruno Ribstein, Jewgenija Muraschko, Christine Sgoff, Junhong Wei, and Ulrich Achatz

resulting in a constant buoyancy frequency . This implies a reference density profile where is the density scale height. Some of the test cases involve a prescribed background jet as an initial mean flow with a half-cosine wave shape: where is the maximal magnitude of the jet initialized at height , and is the width (i.e., vertical extent) of the half-cosine shape. In these cases, the wave-induced mean flow is diagnosed as : that is, the initial mean wind is subtracted from the total mean wind

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Claudia Christine Stephan, Cornelia Strube, Daniel Klocke, Manfred Ern, Lars Hoffmann, Peter Preusse, and Hauke Schmidt

on troposphere–stratosphere exchanges of water vapor, ozone, and other gases ( Baldwin et al. 2001 ), as well as remote effects on global circulation. Deep convective systems are a major source for GWs in the tropics and the summer midlatitudes ( Pfister et al. 1993 ; McLandress et al. 2000 ; Preusse et al. 2001 ; Hoffmann and Alexander 2010 ; Choi et al. 2012 ). Other important tropospheric GW sources are regions of imbalanced flow near jets (e.g., O’Sullivan and Dunkerton 1995 ; Zhang

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Junhong Wei, Gergely Bölöni, and Ulrich Achatz

1. Introduction As one of the most fundamental physical modes in meteorology, gravity waves (GWs) are ubiquitous buoyancy oscillations in the atmosphere. The sources of excited gravity waves include, among others, topographic forcing ( Smith 1980 ; Menchaca and Durran 2017 ), convection ( Alexander et al. 1995 ; Lane et al. 2001 ), the jets ( Zhang 2004 ; Plougonven and Zhang 2014 ; Hien et al. 2018 ), frontal systems ( Snyder et al. 1993 ; Griffiths and Reeder 1996 ), and shear

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Jannik Wilhelm, T. R. Akylas, Gergely Bölöni, Junhong Wei, Bruno Ribstein, Rupert Klein, and Ulrich Achatz

. Miyahara , and M. Takahashi , 2010b : The roles of equatorial trapped waves and internal inertia–gravity waves in driving the quasi-biennial oscillation. Part II: Three-dimensional distribution of wave forcing . J. Atmos. Sci. , 67 , 981 – 997 , . 10.1175/2009JAS3223.1 Kidston , J. , A. A. Scaife , S. C. Hardiman , D. M. Mitchell , N. Butchart , M. P. Baldwin , and L. J. Gray , 2015 : Stratospheric influence on tropospheric jet streams

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