Publications

Latest:

  • Kruse, C. G., Alexander, M. J., Hoffmann, L., van Niekerk, A., Polichtchouk, I., Bacmeister, J. T., Holt, L., Plougonven, R., Šácha, P., Wright, C., Sato, K., Shibuya, R., Gisinger, S., Ern, M., Meyer, C. I., & Stein, O. (2022). Observed and Modeled Mountain Waves from the Surface to the Mesosphere near the Drake Passage, Journal of the Atmospheric Sciences, 79(4), 909-932. https://doi.org/10.1175/JAS-D-21-0252.1
  • Strube, C., Preusse, P., Ern, M., and Riese, M.: Propagation paths and source distributions of resolved gravity waves in ECMWF-IFS analysis fields around the southern polar night jet, Atmos. Chem. Phys., 21, 18641–18668, https://doi.org/10.5194/acp-21-18641-2021, 2021.
  • Ern, M., Diallo, M., Preusse, P., Mlynczak, M. G., Schwartz, M. J., Wu, Q., and Riese, M.: The semiannual oscillation (SAO) in the tropical middle atmosphere and its gravity wave driving in reanalyses and satellite observations, Atmos. Chem. Phys., 21, 13763-13795, https://doi.org/10.5194/acp-21-13763-2021, 2021.
  • Kim, Y.-H., & Achatz, U. (2021). Interaction between stratospheric Kelvin waves and gravity waves in the easterly QBO phase. Geophysical Research Letters, 48, e2021GL095226. https://doi.org/10.1029/2021GL095226

 

Alphabetic Order:

  1. Chen, D., Strube, C., Ern, M., Preusse, P., and Riese, M.: Global analysis for periodic variations in gravity wave squared amplitudes and momentum fluxes in the middle atmosphere, Ann. Geophys., 37, 487-506, https://doi.org/10.5194/angeo-37-487-2019, 2019.
  2. 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 in the vicinity of the polar night jet. J. Geophys. Res. Atmos., pp. 1423–1436, https://doi.org/10.1002/2016JD025621 . (PACOG, SV cooperation)
  3. Ern, M., Diallo, M., Preusse, P., Mlynczak, M. G., Schwartz, M. J., Wu, Q., and Riese, M.: The semiannual oscillation (SAO) in the tropical middle atmosphere and its gravity wave driving in reanalyses and satellite observations, Atmos. Chem. Phys., 21, 13763-13795, https://doi.org/10.5194/acp-21-13763-2021, 2021.
  4. Ern, M., Trinh, Q. T., Kaufmann, M., Krisch, I., Preusse, P., Ungermann, J., Zhu, Y., Gille, J. C., Mlynczak, M. G., Russell III, J. M., Schwartz, M. J., and Riese, M., 2016: Satellite observations of middle atmosphere gravity wave absolute momentum flux and of its vertical gradient during recent stratospheric warmings, Atmos. Chem. Phys., 16, 9983-10019, https://doi.org/10.5194/acp-16-9983-201  pdf
  5. Ern, M., L. Hoffmann, and P. Preusse (2017), Directional gravity wave momentum fluxes in the stratosphere derived from high-resolution AIRS temperature data, Geophys. Res. Lett., 44, 475-485, https://doi.org/10.1002/2016GL072007 pdf
  6. Ern, M., Trinh, Q. T., Preusse, P., Gille, J. C., Mlynczak, M. G., Russell III, J. M., and Riese, M., 2018: GRACILE: a comprehensive climatology of atmospheric gravity wave parameters based on satellite limb soundings, Earth Syst. Sci. Data, 10, 857-892, https://doi.org/10.5194/essd-10-857-2018  pdf
    • Ern, Manfred; Trinh, Quang Thai; Preusse, Peter; Gille, John C; Mlynczak, Martin G; Russell III, James M; Riese, Martin (2017): GRACILE: A comprehensive climatology of atmospheric gravity wave parameters based on satellite limb soundings, link to data in NetCDF format. PANGAEA, https://doi.org/10.1594/PANGAEA.879658 download
  7. Geldenhuys, M., Preusse, P., Krisch, I., Zülicke, C., Ungermann, J., Ern, M., Friedl-Vallon, F., and Riese, M.: Orographically induced spontaneous imbalance within the jet causing a large-scale gravity wave event, Atmos. Chem. Phys., 21, 10393–10412, https://doi.org/10.5194/acp-21-10393-2021, 2021
  8. Kalisch, S., H.-Y. Chun, M. Ern, P. Preusse, Q. T. Trinh, S. D. Eckermann, and M. Riese (2016), Comparison of simulated and observed convective gravity waves, J. Geophys. Res. Atmos., 121, 13474–13492, https://doi.org/10.1002/2016JD025235 pdf
  9. Kim, Y.-H., & Achatz, U. (2021). Interaction between stratospheric Kelvin waves and gravity waves in the easterly QBO phase. Geophysical Research Letters, 48, e2021GL095226. https://doi.org/10.1029/2021GL095226
  10. Kim, Y., Bölöni, G., Borchert, S., Chun, H., & Achatz, U. (2021). Toward Transient Subgrid-Scale Gravity Wave Representation in Atmospheric Models. Part II: Wave Intermittency Simulated with Convective Sources, Journal of the Atmospheric Sciences, 78(4), 1339-1357. https://doi.org/10.1175/JAS-D-20-0066.1
  11. Krisch, I., Ern, M., Hoffmann, L., Preusse, P., Strube, C., Ungermann, J., Woiwode, W., and Riese, M.: Superposition of gravity waves with different propagation characteristics observed by airborne and space-borne infrared sounders, Atmos. Chem. Phys., 20, 11469–11490, https://doi.org/10.5194/acp-20-11469-2020, 2020
  12. Krisch, I., Ungermann, J., Preusse, P., Kretschmer, E., and Riese, M., 2018: Limited angle tomography of mesoscale gravity waves by the infrared limb-sounder GLORIA, Atmos. Meas. Tech., 11, 4327-4344, https://doi.org/10.5194/amt-11-4327-2018
  13. Krisch, I., Preusse, P., Ungermann, J., Dörnbrack, A., Eckermann, S. D., Ern, M., Friedl-Vallon, F., Kaufmann, M., Oelhaf, H., Rapp, M., Strube, C., and Riese, M., 2017: First tomographic observations of gravity waves by the infrared limb imager GLORIA, Atmos. Chem. Phys., 17, 14937-14953, https://doi.org/10.5194/acp-17-14937-2017, pdf
  14. Matthias, V. and Ern, M., 2018: On the origin of the mesospheric quasi-stationary planetary waves in the unusual Arctic winter 2015/2016, Atmos. Chem. Phys., 18, 4803-4815, https://doi.org/10.5194/acp-18-4803-2018 pdf
  15. 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
  16. Stephan, C. C., Strube, C., Klocke, D., Ern, M., Hoffmann, L., Preusse, P., & Schmidt, H. ( 2019). Gravity waves in global high‐resolution simulations with explicit and parameterized convection. Journal of Geophysical Research: Atmospheres, 124, 4446– 4459. https://doi.org/10.1029/2018JD030073
  17. Stephan, C.C., C. Strube, D. Klocke, M. Ern, L. Hoffmann, P. Preusse, and H. Schmidt, 2019: Intercomparison of Gravity Waves in Global Convection-Permitting Models. J. Atmos. Sci., 76, 2739–2759, https://doi.org/10.1175/JAS-D-19-0040.1
  18. Strube, C., Ern, M., Preusse, P., and Riese, M.: Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods, Atmos. Meas. Tech., 13, 4927–4945, https://doi.org/10.5194/amt-13-4927-2020, 2020
  19. Trinh, Q. T., Kalisch, S., Preusse, P., Ern, M., Chun, H.-Y., Eckermann, S. D., Kang, M.-J., and Riese, M., 2016: Tuning of a convective gravity wave source scheme based on HIRDLS observations, Atmos. Chem. Phys., 16, 7335-7356, https://doi.org/10.5194/acp-16-7335-2016 pdf
  20. Yigit, E., Medvedev, A. S, and Ern, M. (2021): Effects of Latitude-Dependent Gravity Wave Source Variations on the Middle and Upper Atmosphere, Front. Astron. Space Sci., 7, 614018, doi: 10.3389/fspas.2020.614018

Data sets:

to paper of Ern et al, 2018:

Ern, Manfred; Trinh, Quang Thai; Preusse, Peter; Gille, John C; Mlynczak, Martin G; Russell III, James M; Riese, Martin (2017): GRACILE: A comprehensive climatology of atmospheric gravity wave parameters based on satellite limb soundings, link to data in NetCDF format. PANGAEA, https://doi.org/10.1594/PANGAEA.879658 download

 

Some insight into the research going on within the project give the abstracts of the publications:

  1. Global analysis for periodic variations in gravity wave squared amplitudes and momentum fluxes in the middle atmosphere, Chen, D., Strube, C., Ern, M., Preusse, P., and Riese, M.; Ann. Geophys., 37, 487-506, https://doi.org/10.5194/angeo-37-487-2019, 2019.
    Atmospheric gravity waves (GWs) are an important coupling mechanism in the middle atmosphere. For instance, they provide a large part of the driving of long-period atmospheric oscillations such as the Quasi-Biennial Oscillation (QBO) and the semiannual oscillation (SAO) and are in turn modulated. They also induce the wind reversal in the mesosphere–lower thermosphere region (MLT) and the residual mean circulation at these altitudes. In this study, the variations in monthly zonal mean gravity wave square temperature amplitudes (GWSTAs) and, for the first time, absolute gravity wave momentum flux (GWMF) on different timescales such as the annual, semiannual, terannual and quasi-biennial variations are investigated by spectrally analyzing SABER observations from 2002 to 2015. Latitude–altitude cross sections of spectral amplitudes and phases of GWSTA and absolute GWMF in the stratosphere and mesosphere are presented and physically interpreted. It is shown that the time series of GWSTA and GWMF at a certain altitude and latitude results from the complex interplay of GW sources, propagation through and filtering in lower altitudes, oblique propagation superposing GWs from different source locations, and, finally, the modulation of the GW spectrum by the winds at a considered altitude and latitude. The strongest component is the annual variation, dominated in the summer hemisphere by subtropical convective sources and in the winter hemisphere by polar vortex dynamics. At heights of the wind reversal, a 180∘ phase shift also occurs, which is at different altitudes for GWSTA and GWMF. In the intermediate latitudes a semiannual variation (SAV) is found. Dedicated GW modeling is used to investigate the nature of this SAV, which is a different phenomenon from the tropical SAO also seen in the data. In the tropics a stratospheric and a mesospheric QBO are found, which are, as expected, in antiphase. Indication for a QBO influence is also found at higher latitudes. In previous studies a terannual variation (TAV) was identified. In the current study we explain its origin. In particular the observed patterns for the shorter periods, SAV and TAV, can only be explained by poleward propagation of GWs from the lower-stratosphere subtropics into the midlatitude and high-latitude mesosphere. In this way, critical wind filtering in the lowermost stratosphere is avoided and this oblique propagation is hence likely an important factor for MLT dynamics.

  2. Horizontal propagation of large amplitude mountain waves in the vicinity of the polar night jet; Ehard, B., B. Kaifler, A. Dörnbrack, P. Preusse, S. Eckermann, M. Bramberger, S. Gisinger, N. Kaifler, B. Liley, J. Wagner, and M. Rapp, 2017: . J. Geophys. Res. Atmos., pp. 1423–1436, 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.

  3. The semiannual oscillation (SAO) in the tropical middle atmosphere and its gravity wave driving in reanalyses and satellite observations: Ern, M., Diallo, M., Preusse, P., Mlynczak, M. G., Schwartz, M. J., Wu, Q., and Riese, M.: , Atmos. Chem. Phys., 21, 13763-13795, <a href="https://doi.org/10.5194/acp-21-13763-2021">https://doi.org/10.5194/acp-21-13763-2021</a>, 2021.<br />Abstract: Gravity waves play a significant role in driving the semiannual oscillation (SAO) of the zonal wind in the tropics. However, detailed knowledge of this forcing is missing, and direct estimates from global observations of gravity waves are sparse. For the period 2002–2018, we investigate the SAO in four different reanalyses: ERA-Interim, JRA-55, ERA-5, and MERRA-2. Comparison with the SPARC zonal wind climatology and quasi-geostrophic winds derived from Microwave Limb Sounder (MLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite observations show that the reanalyses reproduce some basic features of the SAO. However, there are also large differences, depending on the model setup. Particularly, MERRA-2 seems to benefit from dedicated tuning of the gravity wave drag parameterization and assimilation of MLS observations. To study the interaction of gravity waves with the background wind, absolute values of gravity wave momentum fluxes and a proxy for absolute gravity wave drag derived from SABER satellite observations are compared with different wind data sets: the SPARC wind climatology; data sets combining ERA-Interim at low altitudes and MLS or SABER quasi-geostrophic winds at high altitudes; and data sets that combine ERA-Interim, SABER quasi-geostrophic winds, and direct wind observations by the TIMED Doppler Interferometer (TIDI). In the lower and middle mesosphere the SABER absolute gravity wave drag proxy correlates well with positive vertical gradients of the background wind, indicating that gravity waves contribute mainly to the driving of the SAO eastward wind phases and their downward propagation with time. At altitudes 75–85 <span class="inline-formula">km</span>, the SABER absolute gravity wave drag proxy correlates better with absolute values of the background wind, suggesting a more direct forcing of the SAO winds by gravity wave amplitude saturation. Above about 80 <span class="inline-formula">km</span> SABER gravity wave drag is mainly governed by tides rather than by the SAO. The reanalyses reproduce some basic features of the SAO gravity wave driving: all reanalyses show stronger gravity wave driving of the SAO eastward phase in the stratopause region. For the higher-top models ERA-5 and MERRA-2, this is also the case in the lower mesosphere. However, all reanalyses are limited by model-inherent damping in the upper model levels, leading to unrealistic features near the model top. Our analysis of the SABER and reanalysis gravity wave drag suggests that the magnitude of SAO gravity wave forcing is often too weak in the free-running general circulation models; therefore, a more realistic representation is needed.

  4. Satellite observations of middle atmosphere gravity wave absolute momentum flux and of its vertical gradient during recent stratospheric warmings Ern, M., Trinh, Q. T., Kaufmann, M., Krisch, I., Preusse, P., Ungermann, J., Zhu, Y., Gille, J. C., Mlynczak, M. G., Russell III, J. M., Schwartz, M. J., and Riese, M., 2016: , Atmos. Chem. Phys., 16, 9983-10019, https://doi.org/10.5194/acp-16-9983-201  pdf
    Sudden stratospheric warmings (SSWs) are circulation anomalies in the polar region during winter. They mostly occur in the Northern Hemisphere and affect also surface weather and climate. Both planetary waves and gravity waves contribute to the onset and evolution of SSWs. While the role of planetary waves for SSW evolution has been recognized, the effect of gravity waves is still not fully understood, and has not been comprehensively analyzed based on global observations. In particular, information on the gravity wave driving of the background winds during SSWs is still missing.
    We investigate the boreal winters from 2001/2002 until 2013/2014. Absolute gravity wave momentum fluxes and gravity wave dissipation (potential drag) are estimated from temperature observations of the satellite instruments HIRDLS and SABER. In agreement with previous work, we find that sometimes gravity wave activity is enhanced before or around the central date of major SSWs, particularly during vortex-split events. Often, SSWs are associated with polar-night jet oscillation (PJO) events. For these events, we find that gravity wave activity is strongly suppressed when the wind has reversed from eastward to westward (usually after the central date of a major SSW). In addition, gravity wave potential drag at the bottom of the newly forming eastward-directed jet is remarkably weak, while considerable potential drag at the top of the jet likely contributes to the downward propagation of both the jet and the new elevated stratopause. During PJO events, we also find some indication for poleward propagation of gravity waves. Another striking finding is that obviously localized gravity wave sources, likely mountain waves and jet-generated gravity waves, play an important role during the evolution of SSWs and potentially contribute to the triggering of SSWs by preconditioning the shape of the polar vortex. The distribution of these hot spots is highly variable and strongly depends on the zonal and meridional shape of the background wind field, indicating that a pure zonal average view sometimes is a too strong simplification for the strongly perturbed conditions during the evolution of SSWs.

  5. Directional gravity wave momentum fluxes in the stratosphere derived from high-resolution AIRS temperature data, Ern, M., L. Hoffmann, and P. Preusse (2017),  Geophys. Res. Lett., 44, 475-485, https://doi.org/10.1002/2016GL072007
    In order to reduce uncertainties in modeling the stratospheric circulation, global observations of gravity wave momentum flux (GWMF) vectors are required for comparison with distributions of resolved and parametrized GWMF in global models. For the first time, we derive GWMF vectors globally from data of a nadir‐viewing satellite instrument: we apply a 3‐D method to an Atmospheric Infrared Sounder (AIRS) temperature data set that was optimized for gravity wave (GW) analysis. For January 2009, the resulting distributions of GW amplitudes and of net GWMF highlight the importance of GWs in the polar vortex and the summertime subtropics. Net GWMF is preferentially directed opposite to the background wind, and, interestingly, it is dominated by large‐amplitude GWs of relatively long horizontal wavelength. For convective GW sources, these large horizontal scales are in contradiction with traditional thoughts. However, the observational filter effect needs to be kept in mind when interpreting the results.

  6. GRACILE: a comprehensive climatology of atmospheric gravity wave parameters based on satellite limb soundings Ern, M., Trinh, Q. T., Preusse, P., Gille, J. C., Mlynczak, M. G., Russell III, J. M., and Riese, M., 2018: , Earth Syst. Sci. Data, 10, 857-892, https://doi.org/10.5194/essd-10-857-2018
    Gravity waves are one of the main drivers of atmospheric dynamics. The spatial resolution of most global atmospheric models, however, is too coarse to properly resolve the small scales of gravity waves, which range from tens to a few thousand kilometers horizontally, and from below 1 km to tens of kilometers vertically. Gravity wave source processes involve even smaller scales. Therefore, general circulation models (GCMs) and chemistry climate models (CCMs) usually parametrize the effect of gravity waves on the global circulation. These parametrizations are very simplified. For this reason, comparisons with global observations of gravity waves are needed for an improvement of parametrizations and an alleviation of model biases.
    We present a gravity wave climatology based on atmospheric infrared limb emissions observed by satellite (GRACILE). GRACILE is a global data set of gravity wave distributions observed in the stratosphere and the mesosphere by the infrared limb sounding satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Typical distributions (zonal averages and global maps) of gravity wave vertical wavelengths and along-track horizontal wavenumbers are provided, as well as gravity wave temperature variances, potential energies and absolute momentum fluxes. This global data set captures the typical seasonal variations of these parameters, as well as their spatial variations. The GRACILE data set is suitable for scientific studies, and it can serve for comparison with other instruments (ground-based, airborne, or other satellite instruments) and for comparison with gravity wave distributions, both resolved and parametrized, in GCMs and CCMs. The GRACILE data set is available as supplementary data at https://doi.org/10.1594/PANGAEA.879658.

  7. Orographically induced spontaneous imbalance within the jet causing a large-scale gravity wave event; Geldenhuys, M., Preusse, P., Krisch, I., Zülicke, C., Ungermann, J., Ern, M., Friedl-Vallon, F., and Riese, M., Atmos. Chem. Phys., 21, 10393–10412, https://doi.org/10.5194/acp-21-10393-2021, 2021
    To better understand the impact of gravity waves (GWs) on the middle atmosphere in the current and future climate, it is essential to understand their excitation mechanisms and to quantify their basic properties. Here a new process for GW excitation by orography–jet interaction is discussed. In a case study, we identify the source of a GW observed over Greenland on 10 March 2016 during the POLSTRACC (POLar STRAtosphere in a Changing Climate) aircraft campaign. Measurements were taken with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) instrument deployed on the High Altitude Long Range (HALO) German research aircraft. The measured infrared limb radiances are converted into a 3D observational temperature field through the use of inverse modelling and limited-angle tomography. We observe GWs along a transect through Greenland where the GW packet covers ≈ 1/3
    of the Greenland mainland. GLORIA observations indicate GWs between 10 and 13 km of altitude with a horizontal wavelength of 330 km, a vertical wavelength of 2 km and a large temperature amplitude of 4.5 K. Slanted phase fronts indicate intrinsic propagation against the wind, while the ground-based propagation is with the wind. The GWs are arrested below a critical layer above the tropospheric jet. Compared to its intrinsic horizontal group velocity (25–72 m s−1) the GW packet has a slow vertical group velocity of 0.05–0.2 m s−1. This causes the GW packet to propagate long distances while spreading over a large area and remaining constrained to a narrow vertical layer. A plausible source is not only orography, but also out-of-balance winds in a jet exit region and wind shear. To identify the GW source, 3D GLORIA observations are combined with a gravity wave ray tracer, ERA5 reanalysis and high-resolution numerical experiments. In a numerical experiment with a smoothed orography, GW activity is quite weak, indicating that the GWs in the realistic orography experiment are due to orography. However, analysis shows that these GWs are not mountain waves. A favourable area for spontaneous GW emission is identified in the jet by the cross-stream ageostrophic wind, which indicates when the flow is out of geostrophic balance. Backwards ray-tracing experiments trace into the jet and regions where the Coriolis and the pressure gradient forces are out of balance. The difference between the full and a smooth-orography experiment is investigated to reveal the missing connection between orography and the out-of-balance jet. We find that this is flow over a broad area of elevated terrain which causes compression of air above Greenland. The orography modifies the wind flow over large horizontal and vertical scales, resulting in out-of-balance geostrophic components. The out-of-balance jet then excites GWs in order to bring the flow back into balance. This is the first observational evidence of GW generation by such an orography–jet mechanism.

  8. Comparison of simulated and observed convective gravity waves Kalisch, S., H.-Y. Chun, M. Ern, P. Preusse, Q. T. Trinh, S. D. Eckermann, and M. Riese (2016), , J. Geophys. Res. Atmos., 121, 13474–13492, https://doi.org/10.1002/2016JD025235
    Gravity waves (GWs) from convection have horizontal wavelengths typically shorter than 100 km. Resolving these waves in state‐of‐the‐art atmospheric models still remains challenging. Also, their time‐dependent excitation process cannot be represented by a common GW drag parametrization with static launch distribution. Thus, the aim of this paper is to investigate the excitation and three‐dimensional propagation of GWs forced by deep convection in the troposphere and estimate their influence on the middle atmosphere. For that purpose, the GW ray tracer Gravity‐wave Regional Or Global Ray Tracer (GROGRAT) has been coupled to the Yonsei convective GW source model. The remaining free model parameters have been constrained by measurements. This work led to a coupled convective GW model representing convective GWs forced from small cells of deep convection up to large‐scale convective clusters. In order to compare our simulation results with observed global distributions of momentum flux, limitations of satellite instruments were taken into account: The observational filter of a limb‐viewing satellite instrument restricts measurements of GWs to waves with horizontal wavelengths longer than 100 km. Convective GWs, however, often have shorter wavelengths. This effect is taken into account when comparing simulated and observable GW spectra. We find good overall agreement between simulated and observed GW global distributions, if superimposed with a nonorographic background spectrum for higher‐latitude coverage. Our findings indicate that parts of the convective GW spectrum can indeed be observed by limb‐sounding satellites.

  9. Interaction between stratospheric Kelvin waves and gravity waves in the easterly QBO phase: Kim, Y.-H., & Achatz, U. (2021). Geophysical Research Letters, 48, e2021GL095226. https://doi.org/10.1029/2021GL095226
    A general circulation model is used to study the interaction between parameterized gravity waves (GWs) and large-scale Kelvin waves in the tropical stratosphere. The simulation shows that Kelvin waves with substantial amplitudes (∼10 m s−1) can significantly affect the distribution of GW drag by modulating the local shear. Furthermore, this effect is localized to regions above strong convective organizations that generate large-amplitude GWs, so that at a given altitude it occurs selectively in a certain phase of Kelvin waves. Accordingly, this effect also contributes to the zonal-mean GW drag, which is large in the middle stratosphere during the phase transition of the quasi-biennial oscillation (QBO). Furthermore, we detect an enhancement of Kelvin-wave momentum flux due to GW drag modulated by Kelvin waves. The result implies an importance of GW dynamics coupled to Kelvin waves in the QBO progression.
    Plain Language Summary
    The variability of the tropical atmosphere at altitudes of about 18–40 km is dominated by a large-amplitude long-term oscillation of wind, the quasi-biennial oscillation, which has a broad impact on the climate and seasonal forecasting. This oscillation is known to be driven by various types of atmospheric waves with multiple spatial scales. Using a numerical model, this study reports a process of interaction between those waves on different scales, which has not been illuminated before. The result implies a potential importance of this process in the progression of the quasi-biennial oscillation. Proper model representations of these multiscale waves and tropical convection are required to simulate this process.

  10. Towards transient subgrid-scale gravity wave representation in atmospheric models, Part II: Wave intermittency simulated with convective sources: Kim, Y., G. Bölöni, S. Borchert, H. Chun, and U. Achatz,  . J. Atmos. Sci., doi: https://doi.org/10.1175/JAS-D-20-0066.1
    Abstract: In a companion paper, the Multiscale Gravity Wave Model (MS-GWaM) has been introduced and its application to a global model as a transient subgrid-scale parameterization has been described. This paper focuses on the examination of intermittency of gravity waves (GWs) modeled by MS-GWaM. To introduce the variability and intermittency in wave sources, convective GW sources are formulated, using diabatic heating diagnosed by the convection parameterization, and they are coupled to MS-GWaM in addition to a flow-independent source in the extratropics accounting for GWs due neither to convection nor to orography. The probability density function (PDF) and Gini index for GW pseudomomentum fluxes are assessed to investigate the intermittency. Both are similar to those from observations in the lower stratosphere. The intermittency of GWs over tropical convection is quite high and is found not to change much in the vertical direction. In the extratropics, where nonconvective GWs dominate, the intermittency is lower than that in the tropics in the stratosphere and comparable to that in the mesosphere, exhibiting a gradual increase with altitude. The PDFs in these latitudes seem to be close to the lognormal distributions. Effects of transient GW–mean-flow interactions on the simulated GW intermittency are assessed by performing additional simulations using the steady-state assumption in the GW parameterization. The intermittency of parameterized GWs over tropical convection is found to be overestimated by the assumption, whereas in the extratropics it is largely underrepresented. Explanation and discussion of these effects are included.

  11. Superposition of gravity waves with different propagation characteristics observed by airborne and space-borne infrared sounders: Krisch, I., Ern, M., Hoffmann, L., Preusse, P., Strube, C., Ungermann, J., Woiwode, W., and Riese, M., Atmos. Chem. Phys., https://doi.org/10.5194/acp-20-11469-2020
    Many gravity wave analyses, based on either observations or model simulations, assume the presence of only a single dominant wave. This paper shows that there are much more complex cases with gravity waves from multiple sources crossing each others' paths. A complex gravity wave structure consisting of a superposition of multiple wave packets was observed above southern Scandinavia on 28 January 2016 with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). The tomographic measurement capability of GLORIA enabled a detailed 3-D reconstruction of the gravity wave field and the identification of multiple wave packets with different horizontal and vertical scales. The larger-scale gravity waves with horizontal wavelengths of around 400 km could be characterised using a 3-D wave-decomposition method. The smaller-scale wave components with horizontal wavelengths below 200 km were discussed by visual inspection. For the larger-scale gravity wave components, a combination of gravity-wave ray-tracing calculations and ERA5 reanalysis fields identified orography as well as a jet-exit region and a low-pressure system as possible sources. All gravity waves are found to propagate upward into the middle stratosphere, but only the orographic waves stay directly above their source. The comparison with ERA5 also shows that ray tracing provides reasonable results even for such complex cases with multiple overlapping wave packets. Despite their coarser vertical resolution compared to GLORIA measurements, co-located AIRS measurements in the middle stratosphere are in good agreement with the ray tracing and ERA5 results, proving once more the validity of simple ray-tracing models. Thus, this paper demonstrates that the high-resolution GLORIA observations in combination with simple ray-tracing calculations can provide an important source of information for enhancing our understanding of gravity wave propagation.

  12. Limited angle tomography of mesoscale gravity waves by the infrared limb-sounder GLORIA,  Krisch, I., Ungermann, J., Preusse, P., Kretschmer, E., and Riese, M., 2018: Atmos. Meas. Tech., 11, 4327-4344, https://doi.org/10.5194/amt-11-4327-2018
    Three-dimensional measurements of gravity waves are required in order to quantify their direction-resolved momentum fluxes and obtain a better understanding of their propagation characteristics. Such 3-D measurements of gravity waves in the lowermost stratosphere have been provided by the airborne Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) using full angle tomography. Closed flight patterns of sufficient size are needed to acquire the full set of angular measurements for full angle tomography. These take about 2 h and are not feasible everywhere due to scientific reasons or air traffic control restrictions. Hence, this paper investigates the usability of limited angle tomography for gravity wave research based on synthetic observations. Limited angle tomography uses only a limited set of angles for tomographic reconstruction and can be applied to linear flight patterns. A synthetic end-to-end simulation has been performed to investigate the sensitivity of limited angle tomography to gravity waves with different wavelengths and orientations with respect to the flight path. For waves with wavefronts roughly perpendicular to the flight path, limited angle tomography and full angle tomography can derive wave parameters like wavelength, amplitude, and wave orientation with similar accuracy. For waves with a horizontal wavelength above 200 km and vertical wavelength above 3 km, the wavelengths can be retrieved with less than 10 % error, the amplitude with less than 20 % error, and the horizontal wave direction with an error below 10∘. This is confirmed by a comparison of results obtained from full angle tomography and limited angle tomography for real measurements taken on 25 January 2016 over Iceland. The reproduction quality of gravity wave parameters with limited angle tomography, however, depends strongly on the orientation of the waves with respect to the flight path. Thus, full angle tomography might be preferable in cases in which the orientation of the wave cannot be predicted or waves with different orientations exist in the same volume and thus the flight path cannot be adjusted accordingly. Also, for low-amplitude waves and short-scale waves full angle tomography has advantages due to its slightly higher resolution and accuracy.

  13. First tomographic observations of gravity waves by the infrared limb imager GLORIA Krisch, I., Preusse, P., Ungermann, J., Dörnbrack, A., Eckermann, S. D., Ern, M., Friedl-Vallon, F., Kaufmann, M., Oelhaf, H., Rapp, M., Strube, C., and Riese, M., 2017: , Atmos. Chem. Phys., 17, 14937-14953, https://doi.org/10.5194/acp-17-14937-2017
    Atmospheric gravity waves are a major cause of uncertainty in atmosphere general circulation models. This uncertainty affects regional climate projections and seasonal weather predictions. Improving the representation of gravity waves in general circulation models is therefore of primary interest. In this regard, measurements providing an accurate 3-D characterization of gravity waves are needed. Using the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA), the first airborne implementation of a novel infrared limb imaging technique, a gravity wave event over Iceland was observed. An air volume disturbed by this gravity wave was investigated from different angles by encircling the volume with a closed flight pattern. Using a tomographic retrieval approach, the measurements of this air mass at different angles allowed for a 3-D reconstruction of the temperature and trace gas structure. The temperature measurements were used to derive gravity wave amplitudes, 3-D wave vectors, and direction-resolved momentum fluxes. These parameters facilitated the backtracing of the waves to their sources on the southern coast of Iceland. Two wave packets are distinguished, one stemming from the main mountain ridge in the south of Iceland and the other from the smaller mountains in the north. The total area-integrated fluxes of these two wave packets are determined. Forward ray tracing reveals that the waves propagate laterally more than 2000 km away from their source region. A comparison of a 3-D ray-tracing version to solely column-based propagation showed that lateral propagation can help the waves to avoid critical layers and propagate to higher altitudes. Thus, the implementation of oblique gravity wave propagation into general circulation models may improve their predictive skills.

  14. Towards transient subgrid-scale gravity wave representation in atmospheric models. Part II: Wave intermittency simulated with convective sources: Kim, Y., G. Bölöni, S. Borchert, H. Chun, and U. Achatz, J. Atmos. Sci https://doi.org/10.1175/JAS-D-20-0066.1
    In a companion paper, the Multi-Scale Gravity-Wave Model (MS-GWaM) has been introduced and its application to a global model as a transient subgrid-scale parameterization has been described. This paper focuses on the examination of intermittency of gravity waves (GWs) modeled by MS-GWaM. To introduce the variability and intermittency in wave sources, convective GW sources are formulated, using diabatic heating diagnosed by the convection parameterization, and they are coupled to MS-GWaM in addition to a flow-independent source in the extratropics accounting for GWs due neither to convection nor to orography. The probability density function (PDF) and Gini index for GWpseudomomentum fluxes are assessed to investigate the intermittency. Both are similar to those from observations in the lower stratosphere. The intermittency of GWs over tropical convection is quite high and found not to change much in the vertical. In the extratropics, where non-convective GWs dominate, the intermittency is lower than (comparable to) that in the tropics in the stratosphere (mesosphere), exhibiting a gradual increase with altitude. The PDFs in these latitudes seem to be close to the log-normal distributions. Effects of transient GW-mean-flow interactions on the simulated GWintermittency are assessed by performing additional simulations using the steady-state assumption in the GW parameterization. The intermittency of parameterized GWs over tropical convection is found to be overestimated by the assumption, whereas in the extratropics it is largely underrepresented. Explanation and discussion of these effects are included.

  15. On the origin of the mesospheric quasi-stationary planetary waves in the unusual Arctic winter 2015/2016; Matthias, V. and Ern, M., 2018:, Atmos. Chem. Phys., 18, 4803-4815, https://doi.org/10.5194/acp-18-4803-2018
    The midwinter 2015/2016 was characterized by an unusually strong polar night jet (PNJ) and extraordinarily large stationary planetary wave (SPW) amplitudes in the subtropical mesosphere. The aim of this study is, therefore, to find the origin of these mesospheric SPWs in the midwinter 2015/2016 study period. The study duration is split into two periods: the first period runs from late December 2015 until early January 2016 (Period I), and the second period from early January until mid-January 2016 (Period II). While the SPW 1 dominates in the subtropical mesosphere in Period I, it is the SPW 2 that dominates in Period II. There are three possibilities explaining how SPWs can occur in the mesosphere: (1) they propagate upward from the stratosphere, (2) they are generated in situ by longitudinally variable gravity wave (GW) drag, or (3) they are generated in situ by barotropic and/or baroclinic instabilities. Using global satellite observations from the Microwave Limb Sounder (MLS) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) the origin of the mesospheric SPWs is investigated for both time periods. We find that due to the strong PNJ the SPWs were not able to propagate upward into the mesosphere northward of 50∘ N but were deflected upward and equatorward into the subtropical mesosphere. We show that the SPWs observed in the subtropical mesosphere are the same SPWs as in the mid-latitudinal stratosphere. Simultaneously, we find evidence that the mesospheric SPWs in polar latitudes were generated in situ by longitudinally variable GW drag and that there is a mixture of in situ generation by longitudinally variable GW drag and by instabilities at mid-latitudes. Our results, based on observations, show that the abovementioned three mechanisms can act at the same time which confirms earlier model studies. Additionally, the possible contribution from, or impact of, unusually strong SPWs in the subtropical mesosphere to the disruption of the quasi-biennial oscillation (QBO) in the same winter is discussed.

  16. 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.

  17. Gravity waves in global high‐resolution simulations with explicit and parameterized convection; Stephan, C. C., Strube, C., Klocke, D., Ern, M., Hoffmann, L., Preusse, P., & Schmidt, H. ( 2019) . Journal of Geophysical Research: Atmospheres, 124, 4446– 4459. https://doi.org/10.1029/2018JD030073
    Increasing computing resources allow us to run weather and climate models at horizontal resolutions of 1–10 km. At this range, which is often referred to as the convective gray zone, clouds and convective transport are partly resolved, yet models may not achieve a satisfactory performance without convective parameterizations. Meanwhile, large fractions of the gravity wave (GW) spectrum become resolved at these scales. Convectively generated GWs are sensitive to spatiotemporal characteristics of convective cells. This raises the question of how resolved GWs respond to changes in the treatment of convection. Two global simulations with a horizontal grid spacing of 5 km are performed, one with explicit and one with parameterized convection. The latitudinal profiles of absolute zonal‐mean GW momentum flux match well between both model configurations and observations by satellite limb sounders. However, the simulation with explicit convection shows ∼30–50% larger zonal‐mean momentum fluxes in the summer hemisphere subtropics, where convection is the dominant source of GWs. Our results imply that changes in convection associated with the choice of explicit versus parameterized convection can have important consequences for resolved GWs, with broad implications for the circulation and the transport in the middle atmosphere.

  18. Intercomparison of gravity waves in global convection-permitting models; Stephan, C.C., C. Strube, D. Klocke, M. Ern, L. Hoffmann, P. Preusse and H. Schmidt.. J. Atmos. Sci., 2019. https://doi.org/10.1175/JAS-D-19-0040.1
    Large uncertainties remain with respect to the representation of atmospheric gravity waves (GWs) in General Circulation Models (GCMs) with coarse grids. Insufficient parameterizations result from a lack of observational constraints on the parameters used in GW parameterizations as well as from physical inconsistencies between parameterizations and reality. For instance, parameterizations make oversimplifying assumptions about the generation and propagation of GWs. Increasing computational capabilities now allow GCMs to run at grid spacings that are sufficiently fine to resolve a major fraction of the GW spectrum. This study presents the first intercomparison of resolved GW pseudo-momentum fluxes (GWMFs) in global convection-permitting simulations and those derived from satellite observations. Six simulations of three different GCMs are analyzed over the period of one month of August to assess the sensitivity of GWMF to model formulation and horizontal grid spacing. The simulations reproduce detailed observed features of the global GWMF distribution, which can be attributed to realistic GWs from convection, orography and storm tracks. Yet, the GWMF magnitudes differ substantially between simulations. Differences in the strength of convection may help explain differences in the GWMF between simulations of the same model in the summer low latitudes where convection is the primary source. Across models, there is no evidence for a systematic change with resolution. Instead, GWMF is strongly affected by model formulation. The results imply that validating the realism of simulated GWs across the entire resolved spectrum will remain a difficult challenge not least because of a lack of appropriate observational data.

  19. Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods: Strube, C., Ern, M., Preusse, P., and Riese, M., Atmos. Meas. Tech.,https://doi.org/10.5194/amt-13-4927-2020
    Gravity waves are important drivers of dynamic processes in particular in the middle atmosphere. To analyse atmospheric data for gravity wave signals, it is essential to separate gravity wave perturbations from atmospheric variability due to other dynamic processes. Common methods to separate small-scale gravity wave signals from a large-scale background are separation methods depending on filters in either the horizontal or vertical wavelength domain. However, gravity waves are not the only process that could lead to small-scale perturbations in the atmosphere. Recently, concerns have been raised that vertical wavelength filtering can lead to misinterpretation of other wave-like perturbations, such as inertial instability effects, as gravity wave perturbations.
    In this paper we assess the ability of different spectral background removal approaches to separate gravity waves and inertial instabilities using artificial inertial instability perturbations, global model data and satellite observations. We investigate a horizontal background removal (which applies a zonal wavenumber filter with additional smoothing of the spectral components in meridional and vertical direction), a sophisticated filter based on 2D time–longitude spectral analysis (see Ern et al., 2011) and a vertical wavelength Butterworth filter.
    Critical thresholds for the vertical wavelength and zonal wavenumber are analysed. Vertical filtering has to cut deep into the gravity wave spectrum in order to remove inertial instability remnants from the perturbations (down to 6 km cutoff wavelength). Horizontal filtering, however, removes inertial instability remnants in global model data at wavenumbers far lower than the typical gravity wave scales for the case we investigated. Specifically, a cutoff zonal wavenumber of 6 in the stratosphere is sufficient to eliminate inertial instability structures. Furthermore, we show that for infrared limb-sounding satellite profiles it is possible as well to effectively separate perturbations of inertial instabilities from those of gravity waves using a cutoff zonal wavenumber of 6. We generalize the findings of our case study by examining a 1-year time series of SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) data.

  20. Tuning of a convective gravity wave source scheme based on HIRDLS observations; Trinh, Q. T., Kalisch, S., Preusse, P., Ern, M., Chun, H.-Y., Eckermann, S. D., Kang, M.-J., and Riese, M., 2016: , Atmos. Chem. Phys., 16, 7335-7356, https://doi.org/10.5194/acp-16-7335-2016
    Convection as one dominant source of atmospheric gravity waves (GWs) has been the focus of investigation over recent years. However, its spatial and temporal forcing scales are not well known. In this work we address this open issue by a systematic verification of free parameters of the Yonsei convective GW source scheme based on observations from the High Resolution Dynamics Limb Sounder (HIRDLS). The instrument can only see a limited portion of the gravity wave spectrum due to visibility effects and observation geometry. To allow for a meaningful comparison of simulated GWs to observations, a comprehensive filter, which mimics the instrument limitations, is applied to the simulated waves. By this approach, only long horizontal-scale convective GWs are addressed. Results show that spectrum, distribution of momentum flux, and zonal mean forcing of long horizontal-scale convective GWs can be successfully simulated by the superposition of three or four combinations of parameter sets reproducing the observed GW spectrum. These selected parameter sets are different for northern and southern summer. Although long horizontal-scale waves are only part of the full spectrum of convective GWs, the momentum flux of these waves is found to be significant and relevant for the driving of the QBO (quasi-biennial oscillation). The zonal momentum balance is considered in vertical cross sections of GW momentum flux (GWMF) and GW drag (GWD). Global maps of the horizontal distribution of GWMF are considered and consistency between simulated results and HIRDLS observations is found. The latitude dependence of the zonal phase speed spectrum of GWMF and its change with altitude is discussed.

  21. Effects of Latitude-Dependent Gravity Wave Source Variations on the Middle and Upper Atmosphere: Yigit, E., Medvedev, A. S, and Ern, M. (2021): , Front. Astron. Space Sci., 7, 614018, doi: 10.3389/fspas.2020.614018