Multi-Scale Dynamics of Gravity Waves

Publications

• R. A. Akmaev, J. M. Forbes, F.-J. Lübken, D. J. Murphy, and J. Höffner, 2016: Tides in the mesopause region over Antarctica: Comparison of Whole Atmosphere Model simulations with ground-based observations. J. Geophys. Res., 121:1156–1169 https://doi.org/10.1002/2015JD023673
• G. Baumgarten, J. Fiedler, J. Hildebrand, and F.-J. Lübken, 2015: Inertia gravity wave in the stratosphere and mesosphere observed by Doppler wind and temperature lidar. Geophys. Res. Lett., 42:10,929–10,936, https://doi.org/10.1002/2015GL066991
• Baumgarten, K., Gerding, M., and Lübken, F.‐J. ( 2017), Seasonal variation of gravity wave parameters using different filter methods with daylight lidar measurements at midlatitudes, J. Geophys. Res. Atmos., 122, 2683– 2695 https://doi.org/10.1002/2016JD025916
• Baumgarten, K.,  Gerding, M., Baumgarten, G., and Lübken, F.-J., 2018: Temporal variability of tidal and gravity waves during a record long 10-day continuous lidar sounding, Atmos. Chem. Phys., 18, 371-384, https://doi.org/10.5194/acp-18-371-2018
• Baumgarten, K. and Stober, G.: On the evaluation of the phase relation between temperature and wind tides based on ground-based measurements and reanalysis data in the middle atmosphere, Ann. Geophys., 37, 581–602, https://doi.org/10.5194/angeo-37-581-2019, 2019.
• Bramberger, M., A. Dörnbrack, H. Wilms, F. Ewald, and R. Sharman, 2020: Mountain-Wave Turbulence Encounter of the Research Aircraft HALO above Iceland. J. Appl. Meteor. Climatol., 59, 567–588, https://doi.org/10.1175/JAMC-D-19-0079.1
• Bramberger, M., A. Dörnbrack, H. Wilms, S. Gemsa, K. Raynor, and R. Sharman, 2018: Vertically Propagating Mountain Waves—A Hazard for High-Flying Aircraft?. J. Appl. Meteor. Climatol., 57, 1957–1975, https://doi.org/10.1175/JAMC-D-17-0340.1
• Charuvil Asokan, H., Chau, J. L., Larsen, M. F., Conte, J. F., Marino, R., Vierinen, J., and Borchert, S. (2022). Validation of multistatic meteor radar analysis using modeled mesospheric dynamics: An assessment of the reliability of gradients and vertical velocities. Journal of Geophysical Research: Atmospheres, 127, e2021JD036039. https://doi.org/10.1029/2021JD036039
• Charuvil Asokan, H., Chau, J.L., Marino, R., Vierinen, J., Vargas , F., Urco J.M., Clahsen, M. and Jacobi, C. (2022 . Frequency spectra of horizontal winds in the mesosphere and lower thermosphere region from multistatic specular meteor radar observations during the SIMONe 2018 campaign. Earth Planets Space 74, 69 (2022). https://doi.org/10.1186/s40623-022-01620-7
• Chau, J-L-,  J. M. Urco, V. Avsarkisov, J. P. Vierinen, R. Latteck, C. M. Hall und M. Tsutsumi, Four-dimensional quantification of Kelvin-Helmholtz instabilities in the polar summer mesosphere using volumetric radar imaging, Geophys. Res. Lett., 47, doi:10.1029/2019GL086081, 2020
• J. L. Chau, P. Hoffmann, N. M. Pedatella, V. Matthias, and G. Stober, 2015: Upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events. J. Geophys. Res., 120:3084–3096 https://doi.org/10.1002/2015JA020998
• Dörnbrack, A., Eckermann, S. D., Williams, B. P., & Haggerty, J. (2022). Stratospheric Gravity Waves Excited by a Propagating Rossby Wave Train—A DEEPWAVE Case Study, Journal of the Atmospheric Sciences, 79(2), 567-591. https://doi.org/10.1175/JAS-D-21-0057.1
• Dörnbrack, A. (2021). Stratospheric Mountain Waves Trailing across Northern Europe, Journal of the Atmospheric Sciences, 78(9), 2835-2857. https://doi.org/10.1175/JAS-D-20-0312.1
• Dörnbrack, A., S. Gisinger, and B. Kaifler (2017), On the interpretation of gravity wave measurements by groundbased lidars, Atmosphere, 8, 49 (1-22), .https://doi.org/10.3390/atmos8030049 (GW-TP /PACOG)
• Dörnbrack, A., Gisinger, S., Kaifler, N., Portele, T. C., Bramberger, M., Rapp, M., Gerding, M., Söder, J., Žagar, N., and Jelić, D.: Gravity waves excited during a minor sudden stratospheric warming, 2018. Atmos. Chem. Phys., 18, 12915-12931, https://doi.org/10.5194/acp-18-12915-2018
• Ehard, B., P. Achtert, A. Dörnbrack, S. Gisinger, J. Gumbel, M. Khaplanov, M. Rapp, and J. Wagner, 2016: Combination of Lidar and Model Data for Studying Deep Gravity Wave Propagation. Mon. Wea. Rev., 144, 77–98, https://doi.org/10.1175/MWR-D-14-00405.1
• Ehard, B., Kaifler, B., Kaifler, N., and Rapp, M., 2015: Evaluation of methods for gravity wave extraction from middle-atmospheric lidar temperature measurements, Atmos. Meas. Tech., 8, 4645-4655, https://doi.org/10.5194/amt-8-4645-2015
• Ehard, B., B. Kaifler, A. Dörnbrack, P. Preusse, S. Eckermann, M. Bramberger, S. Gisinger, N. Kaifler, B. Liley, J. Wagner, and M. Rapp, 2017: Horizontal propagation of large‐amplitude mountain waves into the polar night jet, J. Geophys. Res. Atmos., 122, 1423– 1436, https://doi.org/10.1002/2016JD025621. (PACOG, SV cooperation)
• M. Gerding, K. Baumgarten, J. Höffner, and F.-J. Lübken. Lidar soundings between 30 and 100 km altitude during day and night for observation of temperatures, gravity waves and tides. EPJ Web of Conferences, 119:13001, 2015.
• Gisinger, S., I. Polichtchouk, A. Dörnbrack, R. Reichert, B. Kaifler, N. Kaifler, M. Rapp, and I. Sandu, 2022: Gravity-Wave-Driven Seasonal Variability of Temperature Differences between ECMWF IFS and Rayleigh Lidar Measurements in the Lee of the Southern Andes, Journal of Geophysical Research: Atmospheres, 127, e2021JD036270. https://doi.org/10.1029/2021JD036270
• Gisinger, S., Wagner, J., and Witschas, B., 2020: Airborne measurements and large-eddy simulations of small-scale gravity waves at the tropopause inversion layer over Scandinavia, Atmos. Chem. Phys., 20, 10091–10109, https://doi.org/10.5194/acp-20-10091-2020, 2020
• Gisinger, S., A. Dörnbrack, V. Matthias, J. D. Doyle, S. D. Eckermann, B. Ehard, L. Hoffmann, B. Kaifler, C. G. Kruse, and M. Rapp, 2017: Atmospheric Conditions during the Deep Propagating Gravity Wave Experiment (DEEPWAVE), Mon. Wea. Rev. 145, 4249-4275. https://doi.org/10.1175/MWR-D-16-0435.1
• Gupta, A., Birner, T., Dörnbrack, A., & Polichtchouk, I. (2021). Importance of gravity wave forcing for springtime southern polar vortex breakdown as revealed by ERA5. Geophysical Research Letters, 48, e2021GL092762. https://doi.org/10.1029/2021GL092762
• Fritts, D. C., M. Taylor, A. Dörnbrack, M. Rapp, B. Kaifler, and S. Gisinger (2015), The deep propagating gravity wave experiment (DEEPWAVE): An airborne and ground-based exploration of gravity wave propagation and effects from their sources throughout the lower and middle atmosphere, Bulletin of the American Meteorological Society, https://doi.org/10.1175/BAMS-D-14-00269.1
• He, M., Y. Yamazaki, P. Hoffmann, C. Hall, M. Tsutsumi, G. Li und J. Chau, 2020: Zonal wavenumber diagnosis of rossby-wave-like oscillations using paired ground-based radars, J. Geophys. Res., 125, https://doi.org/10.1029/2019JD031599
• Kaifler, N., B. Kaifler, A. Dörnbrack, M. Rapp, J. L. Hormaechea, and A. de la Torre, 2020: Lidar observations of large-amplitude mountain waves in the stratosphere above Tierra del Fuego, Argentina. Scientific Reports 10, 14529. https://doi.org/10.1038/s41598-020-71443-7
• B. Kaifler, Lübken, F.‐J., Höffner, J., Morris, R. J., and Viehl, T. P. ( 2015), Lidar observations of gravity wave activity in the middle atmosphere over Davis (69°S, 78°E), Antarctica, J. Geophys. Res. Atmos., 120, 4506– 4521. https://doi.org/10.1002/2014JD022879
• Kaifler, N., Kaifler, B.; Ehard, B.; Gisinger, S.; Dörnbrack, A.; Rapp, M.; Kivi, R.; Kozlovsky, A. (2017): Observational indications of downward-propagating gravity waves in middle atmosphere lidar data, J. Atmos. Solar-Terr. Phys., https://doi.org/10.1016/j.jastp.2017.03.003
• Kivi, R., Dörnbrack, A., Sprenger, M., and H. Vömel, 2020: Far-ranging impact of mountain waves excited over Greenland on stratospheric dehydration and rehydration, Journal of Geophysical Research: Atmospheres, 125, e2020JD033055. https://doi.org/10.1029/2020JD033055
• Kopp, M.,  M. Gerding, J. Höffner, and F.-J. Lübken (2015): Tidal signatures in temperatures derived from daylight lidar soundings above Kühlungsborn (54°N, 12°E). J. Atmos. Solar-Terr. Phys., pages 37–50, https://doi.org/10.1016/j.jastp.2014.09.002
• Lübken. F.-J., Baumgarten, G. and Berger, U. (2021): Long term trends of mesopheric ice layers: A model study, J. Atmos. Solar-Terr. Phys., 105378, doi:10.1016/j.jastp.2020.105378, 2021
• Lübken, F.-J. and Höffner, J.: VAHCOLI, a new concept for lidars: technical setup, science applications, and first measurements, Atmos. Meas. Tech., 14, 3815–3836, https://doi.org/10.5194/amt-14-3815-2021, 2021
• Laskar, F. I., Chau, J. L., Stober, G., Hoffmann, P., Hall, C. M., and Tsutsumi, M. ( 2016), Quasi‐biennial oscillation modulation of the middle‐ and high‐latitude mesospheric semidiurnal tides during August–September, J. Geophys. Res. Space Physics, 121, 4869– 4879, https://doi.org/10.1002/2015JA022065
• F.-J. Lübken, R. Latteck, E. Becker, J. Höffner, and D. Murphy (2016): Using polar mesosphere summer echoes and stratospheric/mesospheric winds to explain summer mesopause jumps in Antarctica. J. Atmos. Solar-Terr. Phys., https://doi.org/10.1016/j.jastp.2016.06.008
• Matthias, V., Shepherd, T. G., Hoffmann, P., and Rapp, M. (2015): The Hiccup: a dynamical coupling process during the autumn transition in the Northern Hemisphere – similarities and differences to sudden stratospheric warmings, Ann. Geophys., 33, 199-206, https://doi.org/10.5194/angeo-33-199-2015
• Mixa, T., Dörnbrack, A., & Rapp, M. (2021). Nonlinear Simulations of Gravity Wave Tunneling and Breaking over Auckland Island, Journal of the Atmospheric Sciences, 78(5), 1567-1582. https://doi.org/10.1175/JAS-D-20-0
• Placke, M., Hoffmann, P., Latteck, R., and Rapp, M. ( 2015), Gravity wave momentum fluxes from MF and meteor radar measurements in the polar MLT region, J. Geophys. Res. Space Physics, 120, 736– 750, https://doi.org/10.1002/2014JA020460
• Placke, M., Hoffmann, P., and Rapp, M., 2015: First experimental verification of summertime mesospheric momentum balance based on radar wind measurements at 69° N, Ann. Geophys., 33, 1091-1096, https://doi.org/10.5194/angeo-33-1091-2015
• Portele, T.C., A. Dörnbrack, J.S. Wagner, S. Gisinger, B. Ehard, P. Pautet, and M. Rapp, 2018: Mountain-Wave Propagation under Transient Tropospheric Forcing: A DEEPWAVE Case Study. Mon. Wea. Rev., 146, 1861–1888, https://doi.org/10.1175/MWR-D-17-0080.1
• Rapp, M., Kaifler, B., Dörnbrack, A., Gisinger, S., Mixa, T., Reichert, R., Kaifler, N., Knobloch, S., Eckert, R., Wildmann, N., Giez, A., Krasauskas, L., Preusse, P., Geldenhuys, M., Riese, M., Woiwode, W., Friedl-Vallon, F., Sinnhuber, B., Torre, A. d. l., Alexander, P., Hormaechea, J. L., Janches, D., Garhammer, M., Chau, J. L., Conte, J. F., Hoor, P., & Engel, A. (2021). SOUTHTRAC-GW: An Airborne Field Campaign to Explore Gravity Wave Dynamics at the World’s Strongest Hotspot, Bulletin of the American Meteorological Society, 102(4), E871-E893. https://doi.org/10.1175/BAMS-D-20-0034.1
• Rapp, M., Dörnbrack, A., and Kaifler, B. 2018: An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data, Atmos. Meas. Tech., 11, 1031-1048, https://doi.org/10.5194/amt-11-1031-2018, 2018.
• Rapp, M., Dörnbrack, A., & Preusse, P. (2018). Large midlatitude stratospheric temperature variability caused by inertial instability: A potential source of bias for gravity wave climatologies. Geophysical Research Letters, 45, 10,682–10,690. https://doi.org/10.1029/2018GL079142
• Reichert, R., Kaifler, B., Kaifler, N., Dörnbrack, A., Rapp, M., & Hormaechea, J. L. (2021). High-cadence lidar observations of middle atmospheric temperature and gravity waves at the Southern Andes hot spot. Journal of Geophysical Research: Atmospheres, 126, e2021JD034683. https://doi.org/10.1029/2021JD034683
• Reyes, P.M., E. Kudeki, G. A. Lehmacher, J. L. Chau und M. A. Milla, 2020: VIPIR and 50 MHz radar studies of gravity wave signatures in 150-km echoes observed at Jicamarca, J. Geophys. Res., 125, https://doi.org/10.1029/2019JA027535
• Schneider, A., Gerding, M., and Lübken, F.-J., 2015: Comparing turbulent parameters obtained from LITOS and radiosonde measurements, Atmos. Chem. Phys., 15, 2159-2166, https://doi.org/10.5194/acp-15-2159-2015
• Schneider, A., Wagner, J., Söder, J., Gerding, M., and Lübken, F.-J., 2017: Case study of wave breaking with high-resolution turbulence measurements with LITOS and WRF simulations, Atmos. Chem. Phys., 17, 7941-7954, https://doi.org/10.5194/acp-17-7941-2017,
• Söder, J., C. Zülicke, M. Gerding & F.-J. Lübken, 2021: High-resolution observations of turbulence distributions across tropopause folds. J. Geophys. Res. Atmos.: in press, doi:10.1029/2020JD033857
• G. Stober, G.,  K. Baumgarten, J. P. McCormack, P. Brown und J. Czarnecki, Comparative study between ground-based observations and NAVGEM-HA reanalysis data in the MLT region, Atmos. Chem. Phys., accepted, 2020
• Strelnikova, I., Almowafy, M., Baumgarten, G., Baumgarten, K., Ern, M., Gerding, M., & Lübken, F. (2021). Seasonal Cycle of Gravity Wave Potential Energy Densities from Lidar and Satellite Observations at 54° and 69°N, Journal of the Atmospheric Sciences, 78(4), 1359-1386. https://doi.org/10.1175/JAS-D-20-0247.1
• Strelnikova, I., G. Baumgarten und F.-J. Lübken, 2020: Advanced hodograph-based analysis technique to derive gravity-waves parameters from lidar observations, Atmos. Meas. Tech., 13, 479-499, https://doi.org/10.5194/amt-13-479-2020
• Vargas, F., Chau, J. L., Charuvil Asokan, H., and Gerding, M.: Mesospheric gravity wave activity estimated via airglow imagery, multistatic meteor radar, and SABER data taken during the SIMONe–2018 campaign, Atmos. Chem. Phys., 21, 13631–13654, https://doi.org/10.5194/acp-21-13631-2021, 2021.
• Wagner, J., Dörnbrack, A., Rapp, M., Gisinger, S., Ehard, B., Bramberger, M., Witschas, B., Chouza, F., Rahm, S., Mallaun, C., Baumgarten, G., and Hoor, P., 2017: Observed versus simulated mountain waves over Scandinavia – improvement of vertical winds, energy and momentum fluxes by enhanced model resolution?, Atmos. Chem. Phys., 17, 4031-4052, https://doi.org/10.5194/acp-17-4031-2017 (PACOG/GW-TP)
• Wildmann, N., R. Eckert, A. Dörnbrack, S. Gisinger, M. Rapp, K. Ohlmann, A. van Niekerk, 2021: In-situ measurements of wind and turbulence by a motor glider in the Andes. J. Atmos. Ocean. Techn., accepted; https://doi.org/10.1175/JTECH-D-20-0137.1
• Wilms, H., Bramberger, M., and A. Dörnbrack, 2020: Observation and Simulation of Mountain Wave Turbulence above Iceland: Turbulence Intensification due to Wave Interference. Q. J. R. Met. Soc., 1– 21. https://doi.org/10.1002/qj.3848
• Wörl, R., Strelnikov, B., Viehl, T. P., Höffner, J., Pautet, P.-D., Taylor, M. J., Zhao, Y., and Lübken, F.-J.: Thermal structure of the mesopause region during the WADIS-2 rocket campaign, Atmos. Chem. Phys., 19, 77–88, https://doi.org/10.5194/acp-19-77-2019, 2019.
• Woiwode, W., Dörnbrack, A., Bramberger, M., Friedl-Vallon, F., Haenel, F., Höpfner, M., Johansson, S., Kretschmer, E., Krisch, I., Latzko, T., Oelhaf, H., Orphal, J., Preusse, P., Sinnhuber, B.-M., and Ungermann, J.: Mesoscale fine structure of a tropopause fold over mountains, Atmos. Chem. Phys., 18, 15643-15667, https://doi.org/10.5194/acp-18-15643-2018, 2018.

The  Publications show most detailed the research going on within the project. The abstracts of the most recent:

High-cadence lidar observations of middle atmospheric temperature and gravity waves at the Southern Andes hot spot: Reichert, R., Kaifler, B., Kaifler, N., Dörnbrack, A., Rapp, M., & Hormaechea, J. L. (2021). Journal of Geophysical Research: Atmospheres, 126, e2021JD034683. https://doi.org/10.1029/2021JD034683
Abstract: The Southern Andes are the strongest hot spot for atmospheric gravity waves (GWs) in the
stratosphere. Yet, until recently, no high-cadence measurements of GWs within the middle atmosphere
were available in this region. Therefore, the COmpact Rayleigh Autonomous Lidar (CORAL) was deployed
to the Estación Astrónomica Río Grande (53.7°S, 67.7°W), Argentina, to obtain temperature profiles up to
100 km altitude. CORAL operates autonomously and obtained measurements during roughly two thirds
of all nights between November 2017 and October 2020. The excellent measurement coverage allows for
the quantification of GW properties at the hot spot with great detail. The hot spot nature of this region is
reflected in nightly mean temperature profiles showing deviations from the monthly mean in the order
of 25–55 K in each winter month. This is connected to winter mean growth rates of GW potential energy
(Ep), which are to our knowledge the largest ever reported in the stratosphere. The monthly mean Ep
profiles show a mesospheric limit of ∼100 Jkg-1, indicating a saturated GW spectrum at altitudes above
60 km. The winter mean power spectral density also reaches the saturation limit here. Moreover, we
investigated the distribution of vertical wavelengths using our novel diagnostic technique WAVELETSCAN. It reveals waves with vertical wavelengths that are mostly between 10 and 16 km but also can
exceed 25 km in rare occasions.

VAHCOLI, a new concept for lidars: technical setup, science applications, and first measurements: Lübken, F.-J. and Höffner, J.: , Atmos. Meas. Tech., 14, 3815–3836, https://doi.org/10.5194/amt-14-3815-2021, 2021 
A new concept for a cluster of compact lidar systems named VAHCOLI (Vertical And Horizontal COverage by LIdars) is presented, which allows for the measurement of temperatures, winds, and aerosols in the middle atmosphere (∼ 10–110 km) with high temporal and vertical resolution of minutes and some tens of meters, respectively, simultaneously covering horizontal scales from a few hundred meters to several hundred kilometers (“four-dimensional coverage”). The individual lidars (“units”) being used in VAHCOLI are based on a diode-pumped alexandrite laser, which is currently designed to detect potassium (λ=770 nm), and on sophisticated laser spectroscopy measuring all relevant frequencies (seeder laser, power laser, backscattered light) with high temporal resolution (2 ms) and high spectral resolution applying Doppler-free spectroscopy. The frequency of the lasers and the narrowband filter in the receiving system are stabilized to typically 10–100 kHz, which is a factor of roughly 10−5 smaller than the Doppler-broadened Rayleigh signal. Narrowband filtering allows for the measurement of Rayleigh and/or resonance scattering separately from the aerosol (Mie) signal during both night and day. Lidars used for VAHCOLI are compact (volume: ∼ 1 m3) and multi-purpose systems which employ contemporary electronic, optical, and mechanical components. The units are designed to autonomously operate under harsh field conditions in remote locations. An error analysis with parameters of the anticipated system demonstrates that temperatures and line-of-sight winds can be measured from the lower stratosphere to the upper mesosphere with an accuracy of ±(0.1–5) K and ±(0.1–10) m s−1, respectively, increasing with altitude. We demonstrate that some crucial dynamical processes in the middle atmosphere, such as gravity waves and stratified turbulence, can be covered by VAHCOLI with sufficient temporal, vertical, and horizontal sampling and resolution. The four-dimensional capabilities of VAHCOLI allow for the performance of time-dependent analysis of the flow field, for example by employing Helmholtz decomposition, and for carrying out statistical tests regarding, for example, intermittency and helicity. The first test measurements under field conditions with a prototype lidar were performed in January 2020. The lidar operated successfully during a 6-week period (night and day) without any adjustment. The observations covered a height range of ∼ 5–100 km and demonstrated the capability and applicability of this unit for the VAHCOLI concept.

Stratospheric Mountain Waves Trailing across Northern Europe: Dörnbrack, A. (2021). , Journal of the Atmospheric Sciences, 78(9), 2835-2857
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. Coexisting 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 widespread coverage of stratospheric mountain waves 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 nonorographic 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 10 K 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 −4.5 and −32.2 m s−1 day−1, respectively.

Importance of gravity wave forcing for springtime southern polar vortex breakdown as revealed by ERA5: Gupta, A., Birner, T., Dörnbrack, A., & Polichtchouk, I. (2021).  Geophysical Research Letters, 48, e2021GL092762. https://doi.org/10.1029/2021GL092762
Abstract: Planetary waves (PWs) and gravity waves (GWs) are the key drivers of middle atmospheric circulation. Insufficient observations and inaccurate model representation of GWs limit our understanding of their stratospheric contributions, especially during the Antarctic polar vortex breakdown. This study employs the strength of the high-resolution ERA5 reanalysis in resolving a broad spectrum of GWs in southern midlatitudes and its ability to estimate their forcing during the breakdown period. Most of the resolved southern hemisphere GWs deposit momentum around 60°S over the Southern Ocean. Further, a zonal momentum budget analysis during the breakdown period reveals that the resolved GW forcing in ERA5 provides as much as one-fourth of the necessary wind deceleration at 60°S, 10 hPa. The parameterized GW drag, mostly from non-orographic sources, provides more than half of the wind deceleration. Both findings highlight the key role of GWs in the vortex breakdown and discuss possibilities for further stratospheric GW analysis.
Plain Language Summary: Strong flow over mountains during winters and instabilities in the southern hemisphere troposphere can excite gravity waves that propagate from near-surface all the way to atmospheric heights of 50–80 km. At these heights, they dissipate momentum and decelerate the strong eastward winds. Knowing the structure and extent of the forcing by these waves can help to better understand their role in driving the stratospheric and mesospheric circulation. However, the net forcing by these waves is not accurately known on account of limited observations and because global climate models cannot sufficiently resolve them. This study illustrates that the high-resolution ERA5 reanalysis, which forms a natural bridge between observations and free running climate models, can be used to estimate the mean forcing due to such gravity waves and can help assess their role in springtime deceleration of polar vortex. Such an analysis was not possible using previous reanalysis datasets due to low resolution. The findings show that, indeed, gravity wave forcing can provide a large fraction of the deceleration needed to slow down the strong westerly winds in late winters.

Nonlinear Simulations of Gravity Wave Tunneling and Breaking over Auckland Island: Mixa, T., Dörnbrack, A., & Rapp, M. (2021). , Journal of the Atmospheric Sciences, 78(5), 1567-1582. https://doi.org/10.1175/JAS-D-20-0230.1
Abstract: Horizontally dispersing gravity waves with horizontal wavelengths of 30–40 km were observed at mesospheric altitudes over Auckland Island by the airborne advanced mesospheric temperature mapper during a Deep Propagating Gravity Wave Experiment (DEEPWAVE) research flight on 14 July 2014. A 3D nonlinear compressible model is used to determine which propagation conditions enabled gravity wave penetration into the mesosphere and how the resulting instability characteristics led to widespread momentum deposition. Results indicate that linear tunneling through the polar night jet enabled quick gravity wave propagation from the surface up to the mesopause, while subsequent instability processes reveal large rolls that formed in the negative shear above the jet maximum and led to significant momentum deposition as they descended. This study suggests that gravity wave tunneling is a viable source for this case and other deep propagation events reaching the mesosphere and lower thermosphere.

An Airborne Field Campaign to Explore Gravity Wave Dynamics at the World’s Strongest Hotspot SOUTHTRAC-GW: Rapp, M., et al.. (2021)., Bulletin of the American Meteorological Society, 102(4), E871-E893. https://doi.org/10.1175/BAMS-D-20-0034.1
Abstract: The southern part of South America and the Antarctic peninsula are known as the world’s strongest hotspot region of stratospheric gravity wave (GW) activity. Large tropospheric winds are deflected by the Andes and the Antarctic Peninsula and excite GWs that might propagate into the upper mesosphere. Satellite observations show large stratospheric GW activity above the mountains, the Drake Passage, and in a belt centered along 60°S. This scientifically highly interesting region for studying GW dynamics was the focus of the Southern Hemisphere Transport, Dynamics, and Chemistry–Gravity Waves (SOUTHTRAC-GW) mission. The German High Altitude and Long Range Research Aircraft (HALO) was deployed to Rio Grande at the southern tip of Argentina in September 2019. Seven dedicated research flights with a typical length of 7,000 km were conducted to collect GW observations with the novel Airborne Lidar for Middle Atmosphere research (ALIMA) instrument and the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) limb sounder. While ALIMA measures temperatures in the altitude range from 20 to 90 km, GLORIA observations allow characterization of temperatures and trace gas mixing ratios from 5 to 15 km. Wave perturbations are derived by subtracting suitable mean profiles. This paper summarizes the motivations and objectives of the SOUTHTRAC-GW mission. The evolution of the atmospheric conditions is documented including the effect of the extraordinary Southern Hemisphere sudden stratospheric warming (SSW) that occurred in early September 2019. Moreover, outstanding initial results of the GW observation and plans for future work are presented.

Until 2020:

Advanced hodograph-based analysis technique to derive gravity-waves parameters from lidar observations: Strelnikova, I., G. Baumgarten und F.-J. Lübken, Atmos. Meas. Tech., doi:10.5194/amt-13-479-2020, 2020

An advanced hodograph-based analysis technique to derive gravity-wave (GW) parameters from observations of temperature and winds is developed and presented as a step-by-step recipe with justification for every step in such an analysis. As the most adequate background removal technique the 2-D FFT is suggested. For an unbiased analysis of fluctuation whose amplitude grows with height exponentially, we propose applying a scaling function of the form exp (z∕(ςH)), where H is scale height, z is altitude, and the constant ς can be derived by a linear fit to the fluctuation profile and should be in the range 1–10. The most essential part of the proposed analysis technique consists of fitting cosine waves to simultaneously measured profiles of zonal and meridional winds and temperature and subsequent hodograph analysis of these fitted waves. The linear wave theory applied in this analysis is extended by introducing a wave packet envelope term exp(−(z−z0)2/2σ2) that accounts for limited extent of GWs in the observational data set. The novelty of our approach is that its robustness ultimately allows for automation of the hodograph analysis and resolves many more GWs than can be inferred by the manually applied hodograph technique. This technique allows us to unambiguously identify upward- and downward-propagating GWs and their parameters. This technique is applied to unique lidar measurements of temperature and horizontal winds measured in an altitude range of 30 to 70 km.

Lidar observations of large-amplitude mountain waves in the stratosphere above Tierra del Fuego, Argentina: Kaifler, N., B. Kaifler, A. Dörnbrack, M. Rapp, J. L. Hormaechea, and A. de la Torre, 2020, Scientific Reports 10, https://doi.org/10.1038/s41598-020-71443-7

Large-amplitude internal gravity waves were observed using Rayleigh lidar temperature soundings above Rio Grande, Argentina (54∘S, 68∘W), in the period 16–23 June 2018. Temperature perturbations in the upper stratosphere amounted to 80 K peak-to-peak and potential energy densities exceeded 400 J/kg. The measured amplitudes and phase alignments agree well with operational analyses and short-term forecasts of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF), implying that these quasi-steady gravity waves resulted from the airflow across the Andes. We estimate gravity wave momentum fluxes larger than 100 mPa applying independent methods to both lidar data and IFS model data. These mountain waves deposited momentum at the inner edge of the polar night jet and led to a long-lasting deceleration of the stratospheric flow. The accumulated mountain wave drag affected the stratospheric circulation several thousand kilometers downstream. In the 2018 austral winter, mountain wave events of this magnitude contributed more than 30% of the total potential energy density, signifying their importance by perturbing the stratospheric polar vortex.

Airborne measurements and large-eddy simulations of small-scale gravity waves at the tropopause inversion layer over Scandinavia: Gisinger, S., Wagner, J., and Witschas, B., 2020 Atmos. Chem. Phys.,https://doi.org/10.519/acp-20-10091-2020

Coordinated airborne measurements were performed by two research aircraft – Deutsches Zentrum für Luft- und Raumfahrt (DLR) Falcon and High Altitude and Long Range Aircraft (HALO) – in Scandinavia during the GW-LCYCLE II (Investigation of the life cycle of gravity waves) campaign in 2016 to investigate gravity wave processes in the upper troposphere and lower stratosphere (UTLS) region. A mountain wave event was probed over southern Scandinavia on 28 January 2016. The collected dataset constitutes a valuable combination of in situ measurements and horizontal- and altitude-resolved Doppler wind lidar and water vapour measurements with the differential absorption lidar (DIAL). In situ data at different flight altitudes and downward-pointing wind lidar measurements show pronounced changes of the horizontal scales in the vertical velocity field and of the leg-averaged momentum fluxes (MFs) in the UTLS region. The vertical velocity field was dominated by small horizontal scales with a decrease from around 20 to < 10 km in the vicinity of the tropopause inversion layer (TIL). These small scales were also found in the water vapour data and backscatter data of the DIAL. The leg-averaged MF profile determined from the wind lidar data is characterized by a pronounced kink of positive fluxes in the TIL and negative fluxes below. The largest contributions to the MF are from waves with scales > 30 km. The combination of the observations and idealized large-eddy simulations revealed the occurrence of interfacial waves having scales < 10 km on the tropopause inversion during the mountain wave event. The contribution of the interfacial waves to the leg-averaged MF is basically zero due to the phase relationship of their horizontal and vertical velocity perturbations. Interfacial waves have already been observed on boundary-layer inversions but their concept has not been applied to tropopause inversions so far. Our idealized simulations reveal that the TIL affects the vertical trend of leg-averaged MF of mountain waves and that interfacial waves can occur also on tropopause inversions. Our analyses of the horizontal- and altitude-resolved airborne observations confirm that interfacial waves actually do occur in the TIL. As predicted by linear theory, the horizontal scale of those waves is determined by the wind and stability conditions above the inversion. They are found downstream of the main mountain peaks and their MF profile varies around zero and can clearly be distinguished from the MF profile of Kelvin–Helmholtz instability. Further, the idealized large-eddy simulations reveal that the presence of the TIL is crucial in producing this kind of trapped wave at tropopause altitude.

Temporal variability of tidal and gravity waves during a record long 10-day continuous lidar sounding, 2018; Baumgarten, K., Gerding, M., Baumgarten, G., and Lübken, F.-J.; Atmos. Chem. Phys.m https://doi.org/10.5194/acp-18-371-2018

Gravity waves (GWs) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The propagation of gravity waves is strongly affected by tidal waves as they modulate the mean background wind field and vice versa, which is not yet fully understood and not adequately implemented in many circulation models. The daylight-capable Rayleigh–Mie–Raman (RMR) lidar at Kühlungsborn (54∘ N, 12∘ E) typically provides temperature data to investigate both wave phenomena during one full day or several consecutive days in the middle atmosphere between 30 and 75 km altitude. Outstanding weather conditions in May 2016 allowed for an unprecedented 10-day continuous lidar measurement, which shows a large variability of gravity waves and tides on timescales of days. Using a one-dimensional spectral filtering technique, gravity and tidal waves are separated according to their specific periods or vertical wavelengths, and their temporal evolution is studied. During the measurement period a strong 24 h wave occurs only between 40 and 60 km and vanishes after a few days. The disappearance is related to an enhancement of gravity waves with periods of 4–8 h. Wind data provided by ECMWF are used to analyze the meteorological situation at our site. The local wind structure changes during the observation period, which leads to different propagation conditions for gravity waves in the last days of the measurement period and therefore a strong GW activity. The analysis indicates a further change in wave–wave interaction resulting in a minimum of the 24 h tide. The observed variability of tides and gravity waves on timescales of a few days clearly demonstrates the importance of continuous measurements with high temporal and spatial resolution to detect interaction phenomena, which can help to improve parametrization schemes of GWs in general circulation models.

Vertically Propagating Mountain Waves—A Hazard for High-Flying Aircraft?; 2018; Bramberger, M., A. Dörnbrack, H. Wilms, S. Gemsa, K. Raynor, and R. Sharman, J. Appl. Meteor. Climatol https://doi.org/10.1175/JAMC-D-17-0340.1

Stall warnings at flight level 410 (12.5 km) occurred unexpectedly during a research flight of the High Altitude and Long Range Research Aircraft (HALO) over Italy on 12 January 2016. The dangerous flight situation was mitigated by pilot intervention. At the incident location, the stratosphere was characterized by large horizontal variations in the along-track wind speed and temperature. On this particular day, strong northwesterly winds in the lower troposphere in concert with an aligned polar front jet favored the excitation and vertical propagation of large-amplitude mountain waves at and above the Apennines in Italy. These mountain waves carried large vertical energy fluxes of 8 W m−2 and propagated without significant dissipation from the troposphere into the stratosphere. While turbulence is a well-acknowledged hazard to aviation, this case study reveals that nonbreaking, vertically propagating mountain waves also pose a potential hazard, especially to high-flying aircraft. It is the wave-induced modulation of the ambient along-track wind speed that may decrease the aircraft speed toward the minimum needed stall speed.

Gravity waves excited during a minor sudden stratospheric warming. Dörnbrack, A., Gisinger, S., Kaifler, N., Portele, T. C., Bramberger, M., Rapp, M., Gerding, M., Söder, J., Žagar, N., and Jelić, D., Atmos. Chem. Phys, 2018 https://doi.org/10.5194/acp-18-12915-2018

An exceptionally deep upper-air sounding launched from Kiruna airport (67.82∘ N, 20.33∘ E) on 30 January 2016 stimulated the current investigation of internal gravity waves excited during a minor sudden stratospheric warming (SSW) in the Arctic winter 2015/16. The analysis of the radiosonde profile revealed large kinetic and potential energies in the upper stratosphere without any simultaneous enhancement of upper tropospheric and lower stratospheric values. Upward-propagating inertia-gravity waves in the upper stratosphere and downward-propagating modes in the lower stratosphere indicated a region of gravity wave generation in the stratosphere. Two-dimensional wavelet analysis was applied to vertical time series of temperature fluctuations in order to determine the vertical propagation direction of the stratospheric gravity waves in 1-hourly high-resolution meteorological analyses and short-term forecasts. The separation of upward- and downward-propagating waves provided further evidence for a stratospheric source of gravity waves. The scale-dependent decomposition of the flow into a balanced component and inertia-gravity waves showed that coherent wave packets preferentially occurred at the inner edge of the Arctic polar vortex where a sub-vortex formed during the minor SSW.

Mountain-Wave Propagation under Transient Tropospheric Forcing: A DEEPWAVE Case Study, 2018, Portele, T.C., A. Dörnbrack, et al. Mon. Wea. Rev., https://doi.org/10.1175/MWR-D-17-0080.1

The impact of transient tropospheric forcing on the deep vertical mountain-wave propagation is investigated by a unique combination of in situ and remote sensing observations and numerical modeling. The temporal evolution of the upstream low-level wind follows approximately a shape and was controlled by a migrating trough and connected fronts. Our case study reveals the importance of the time-varying propagation conditions in the upper troposphere and lower stratosphere (UTLS). Upper-tropospheric stability, the wind profile, and the tropopause strength affected the observed and simulated wave response in the UTLS. Leg-integrated along-track momentum fluxes () and amplitudes of vertical displacements of air parcels in the UTLS reached up to 130 kN m−1 and 1500 m, respectively. Their maxima were phase shifted to the maximum low-level forcing by ≈8 h. Small-scale waves ( km) were continuously forced, and their flux values depended on wave attenuation by breaking and reflection in the UTLS region. Only maximum flow over the envelope of the mountain range favored the excitation of longer waves that propagated deeply into the mesosphere. Their long propagation time caused a retarded enhancement of observed mesospheric gravity wave activity about 12–15 h after their observation in the UTLS. For the UTLS, we further compared observed and simulated with fluxes of 2D quasi-steady runs. UTLS momentum fluxes seem to be reproducible by individual quasi-steady 2D runs, except for the flux enhancement during the early decelerating forcing phase.

An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data. 2018; Rapp, M., Dörnbrack, A., and Kaifler, B. Atmos. Meas. Tech. https://doi.org/10.5194/amt-11-1031-2018

Temperature profiles based on radio occultation (RO) measurements with the operational European METOP satellites are used to derive monthly mean global distributions of stratospheric (20–40km) gravity wave (GW) potential energy densities (EP) for the period July 2014–December 2016. In order to test whether the sampling and data quality of this data set is sufficient for scientific analysis, we investigate to what degree the METOP observations agree quantitatively with ECMWF operational analysis (IFS data) and reanalysis (ERA-Interim) data. A systematic comparison between corresponding monthly mean temperature fields determined for a latitude–longitude–altitude grid of 5° by 10° by 1km is carried out. This yields very low systematic differences between RO and model data below 30km (i.e., median temperature differences is between −0.2 and +0.3K), which increases with height to yield median differences of +1.0K at 34km and +2.2K at 40km. Comparing EP values for three selected locations at which also ground-based lidar measurements are available yields excellent agreement between RO and IFS data below 35km. ERA-Interim underestimates EP under conditions of strong local mountain wave forcing over northern Scandinavia which is apparently not resolved by the model. Above 35km, RO values are consistently much larger than model values, which is likely caused by the model sponge layer, which damps small-scale fluctuations above  ∼32km altitude. Another reason is the well-known significant increase of noise in RO measurements above 35km. The comparison between RO and lidar data reveals very good qualitative agreement in terms of the seasonal variation of EP, but RO values are consistently smaller than lidar values by about a factor of 2. This discrepancy is likely caused by the very different sampling characteristics of RO and lidar observations. Direct comparison of the global data set of RO and model EP fields shows large correlation coefficients (0.4–1.0) with a general degradation with increasing altitude. Concerning absolute differences between observed and modeled EP values, the median difference is relatively small at all altitudes (but increasing with altitude) with an exception between 20 and 25km, where the median difference between RO and model data is increased and the corresponding variability is also found to be very large. The reason for this is identified as an artifact of the EP algorithm: this erroneously interprets the pronounced climatological feature of the tropical tropopause inversion layer (TTIL) as GW activity, hence yielding very large EP values in this area and also large differences between model and observations. This is because the RO data show a more pronounced TTIL than IFS and ERA-Interim. We suggest a correction for this effect based on an estimate of this "artificial" EP using monthly mean zonal mean temperature profiles. This correction may be recommended for application to data sets that can only be analyzed using a vertical background determination method such as the METOP data with relatively scarce sampling statistics. However, if the sampling statistics allows, our analysis also shows that in general a horizontal background determination is advantageous in that it better avoids contributions to EP that are not caused by gravity waves.

Large midlatitude stratospheric temperature variability caused by inertial instability: A potential source of bias for gravity wave climatologies, 2018; Rapp, M., Dörnbrack, A., & Preusse, P. Geophysical Research Letters, https://doi.org/10.1029/2018GL079142

Stratospheric temperature perturbations (TP) that have previously been misinterpreted as due to gravity waves are revisited. The perturbations observed by radio occultations during December 2015 had peak‐to‐peak amplitudes of 10 K extending from the equator to midlatitudes. The vertically stacked and horizontally flat structures had a vertical wavelength of 12 km. The signs of the TP were 180∘ phase shifted between equatorial and midlatitudes at fixed altitude levels. High‐resolution operational analyses reveal that these shallow temperature structures were caused by inertial instability due to the large meridional shear of the polar night jet at its equatorward flank in combination with Rossby wave breaking. Large stratospheric TP owing to inertial instability do frequently occur in the Northern Hemisphere (Southern Hemisphere) from October to April (April to October) in the 39 years of ECMWF Re‐Analysis‐Interim data. During 10% of the days, TP exceed 5 K (peak to peak).
Plain Language Summary: The stratosphere is the part of the atmosphere between altitudes of ∼15–50 km which contains the ozone layer that shields life from hazardous radiation. We use global stratospheric temperature measurements to learn about the variability of temperatures on vertical scales < 15 km. Usually, it is thought that such variations are caused by waves that are excited by the displacement of air when being lofted upward when, for example, the wind blows over mountains. The air then starts oscillating around its original height level because of gravity. Gravity waves are an important driver of stratospheric winds which, for example, determine the distribution of ozone. We present observations of large stratospheric temperature perturbations which could easily be misinterpreted as gravity waves. Combining the measurements with output of a numerical weather prediction model, we show that the observations are caused by a large‐scale atmospheric instability called inertial instability. Using meteorological data spanning the past 40 years, we quantify when and how often such temperature perturbations of a certain size occur. Our results are important for properly constructing gravity wave climatologies (where inertial instability events must be excluded)—which are in turn an important input for the correct formulation of climate models.

Seasonal variation of gravity wave parameters using different filter methods with daylight lidar measurements at mid-latitudes, Baumgarten, K., Gerding, M., and Lübken, F.‐J. ( 2017), , J. Geophys. Res. Atmos., https://doi.org/10.1002/2016JD025916

The daylight‐capable Rayleigh‐Mie‐Raman (RMR) lidar at the midlatitude station in Kühlungsborn (54°N, 12°E) is in operation since 2010. The RMR lidar system is used to investigate different fractions of atmospheric waves, like gravity waves (GW) and thermal tides (with diurnal, semidiurnal, and terdiurnal components) at day and night. About 6150 h of data have been acquired until 2015. The general challenge for GW observations is the separation of different wave contributions from the observed superposition of GW, tides, or even longer periodic waves. Unfiltered lidar data always include such a superposition. We applied a Butterworth filter to separate GW and tides by vertical wavelength with a cutoff wavelength of 15 km and by observed periods with a cutoff period of 8 h. GW activity and characteristics are derived in an altitude range between 30 and 70 km. The retrieved vertically filtered temperature deviations contain GW with small vertical wavelengths over a broad range of periods, while only a small range of periods is included in the temporally filtered temperature deviations. We observe an annual variation of the wave activity for unfiltered and vertically filtered data, which is caused from tides and inertia gravity waves. In contrast to that, filtering in time leads to a weak semiannual variation for gravity waves with periods of 4–8 h, especially in higher altitudes. During summer, these waves have the half of the total amount of the potential energy budget compared to the unfiltered data. This shows the importance of waves with periods smaller than 8 h.

On the interpretation of gravity wave measurements by groundbased lidars, Dörnbrack, A., S. Gisinger, and B. Kaifler, Atmosphere (2017) .https://doi.org/10.3390/atmos8030049

This paper asks the simple question: How can we interpret vertical time series of middle atmosphere gravity wave measurements by ground-based temperature lidars? Linear wave theory is used to show that the association of identified phase lines with quasi-monochromatic waves should be considered with great care. The ambient mean wind has a substantial effect on the inclination of the detected phase lines. The lack of knowledge about the wind might lead to a misinterpretation of the vertical propagation direction of the observed gravity waves. In particular, numerical simulations of three archetypal atmospheric mountain wave regimes show a sensitivity of virtual lidar observations on the position relative to the mountain and on the scale of the mountain.

Horizontal propagation of large‐amplitude mountain waves into the polar night jet, 2017,  Ehard, B., B. Kaifler, A. Dörnbrack, P. Preusse, et al., J. Geophys. Res. Atmos., https://doi.org/10.1002/2016JD025621

We analyze a large‐amplitude mountain wave event, which was observed by a ground‐based lidar above New Zealand between 31 July and 1 August 2014. Besides the lidar observations, European Centre for Medium‐Range Weather Forecasts (ECMWF) data, satellite observations, and ray tracing simulations are utilized in this study. It is found that the propagation of mountain waves into the middle atmosphere is influenced by two different processes at different stages of the event. At the beginning of the event, instabilities in a weak wind layer cause wave breaking in the lower stratosphere. During the course of the event the mountain waves propagate to higher altitudes and are refracted southward toward the polar night jet due to the strong meridional shear of the zonal wind. As the waves propagate out of the observational volume, the ground‐based lidar observes no mountain waves in the mesosphere. Ray tracing simulations indicate that the mountain waves propagated to mesospheric altitudes south of New Zealand where the polar night jet advected the waves eastward. These results underline the importance of considering horizontal propagation of gravity waves, e.g., when analyzing locally confined observations of gravity waves.

 Atmospheric Conditions during the Deep Propagating Gravity Wave Experiment (DEEPWAVE), 2017; Gisinger, S., A. Dörnbrack, et al., Mon. Wea. Rev., https://doi.org/10.1175/MWR-D-16-0435.1

This paper describes the results of a comprehensive analysis of the atmospheric conditions during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) campaign in austral winter 2014. Different datasets and diagnostics are combined to characterize the background atmosphere from the troposphere to the upper mesosphere. How weather regimes and the atmospheric state compare to climatological conditions is reported upon and how they relate to the airborne and ground-based gravity wave observations is also explored. Key results of this study are the dominance of tropospheric blocking situations and low-level southwesterly flows over New Zealand during June–August 2014. A varying tropopause inversion layer was found to be connected to varying vertical energy fluxes and is, therefore, an important feature with respect to wave reflection. The subtropical jet was frequently diverted south from its climatological position at 30°S and was most often involved in strong forcing events of mountain waves at the Southern Alps. The polar front jet was typically responsible for moderate and weak tropospheric forcing of mountain waves. The stratospheric planetary wave activity amplified in July leading to a displacement of the Antarctic polar vortex. This reduced the stratospheric wind minimum by about 10 m s−1 above New Zealand making breaking of large-amplitude gravity waves more likely. Satellite observations in the upper stratosphere revealed that orographic gravity wave variances for 2014 were largest in May–July (i.e., the period of the DEEPWAVE field phase).

Observational indications of downward-propagating gravity waves in middle atmosphere lidar data, 2017; Kaifler, N., Kaifler, B.; Ehard,et al., J. Atmos. Solar-Terr. Phys., https://doi.org/10.1016/j.jastp.2017.03.003

Two Rayleigh lidars were employed at a southern-hemisphere mid-latitude site in New Zealand (45°S) and a northern-hemisphere high-latitude site in Finland (67°N) in order to observe gravity waves between 30 and 85 km altitude under wintertime conditions. Two-dimensional wavelet analysis is used to analyze temperature perturbations caused by gravity waves and to determine their vertical wavelengths and phase progression. In both datasets, upward phase progression waves occur frequently between 30 and 85 km altitude. Six cases of large-amplitude wave packets are selected which exhibit upward phase progression in the stratosphere and/or mesosphere. We argue that these wave packets propagate downward and we discuss possible wave generation mechanisms. Spectral analysis reveals that superpositions of two or three wave packets are common. Furthermore, their characteristics often match those of upward-propagating waves which are observed at the same time or earlier. In the dataset means, the contribution of upward phase progression waves to the potential energy density Ep is largest in the lower stratosphere above Finland. There, Ep of upward and downward phase progression waves is comparable. At 85 km one third of the potential energy carried by propagating waves is attributed to upward phase progression waves. In some cases Ep of upward phase progression waves far exceeds Ep of downward phase progression waves. The downward-propagating waves might be generated in situ in the middle atmosphere or arise from reflection of upward-propagating waves.

Case study of wave breaking with high-resolution turbulence measurements with LITOS and WRF simulations, 2017; Schneider, A., Wagner, J., Söder, J., Gerding, M., and Lübken, F.-J., Atmos. Chem. Phys., https://doi.org/10.5194/acp-17-7941-2017

Measurements of turbulent energy dissipation rates obtained from wind fluctuations observed with the balloon-borne instrument LITOS (Leibniz-Institute Turbulence Observations in the Stratosphere) are combined with simulations with the Weather Research and Forecasting (WRF) model to study the breakdown of waves into turbulence. One flight from Kiruna (68°N, 21°E) and two flights from Kühlungsborn (54°N, 12°E) are analysed. Dissipation rates are of the order of 0. 1 mW kg−1 (∼ 0.01K d−1) in the troposphere and in the stratosphere below 15km, increasing in distinct layers by about 2 orders of magnitude. For one flight covering the stratosphere up to ∼ 28km, the measurement shows nearly no turbulence at all above 15km. Another flight features a patch with highly increased dissipation directly below the tropopause, collocated with strong wind shear and wave filtering conditions. In general, small or even negative Richardson numbers are affirmed to be a sufficient condition for increased dissipation. Conversely, significant turbulence has also been observed in the lower stratosphere under stable conditions. Observed energy dissipation rates are related to wave patterns visible in the modelled vertical winds. In particular, the drop in turbulent fraction at 15km mentioned above coincides with a drop in amplitude in the wave patterns visible in the WRF. This indicates wave saturation being visible in the LITOS turbulence data.

 Observed versus simulated mountain waves over Scandinavia – improvement of vertical winds, energy and momentum fluxes by enhanced model resolution?, 2017; Wagner, J., Dörnbrack, A., Rapp, M., Gisinger, S., Ehard, B., Bramberger, M., et al., Atmos. Chem. Phys., https://doi.org/10.5194/acp-17-4031-2017

Two mountain wave events, which occurred over northern Scandinavia in December 2013 are analysed by means of airborne observations and global and mesoscale numerical simulations with horizontal mesh sizes of 16, 7.2, 2.4 and 0.8km. During both events westerly cross-mountain flow induced upward-propagating mountain waves with different wave characteristics due to differing atmospheric background conditions. While wave breaking occurred at altitudes between 25 and 30km during the first event due to weak stratospheric winds, waves propagated to altitudes above 30km and interfacial waves formed in the troposphere at a stratospheric intrusion layer during the second event. Global and mesoscale simulations with 16 and 7.2km grid sizes were not able to simulate the amplitudes and wavelengths of the mountain waves correctly due to unresolved mountain peaks. In simulations with 2.4 and 0.8km horizontal resolution, mountain waves with horizontal wavelengths larger than 15km were resolved, but exhibited too small amplitudes and too high energy and momentum fluxes. Simulated fluxes could be reduced by either increasing the vertical model grid resolution or by enhancing turbulent diffusion in the model, which is comparable to an improved representation of small-scale nonlinear wave effects.