Project B06:
Impact of small-scale dynamics on UTLS transport and mixing

Brief Summary

In the tropopause region, gravity waves are small scale fluctuations of the three-dimensional wind, temperature and pressure. Resulting from different sources these waves are essential for two reasons:

(i) they are major drivers of the large scale circulation in the middle and upper atmosphere;

(ii) they can break or dissipate which leads to mixing between air masses.

While the latter is important for the distribution of chemical substances around the region of the breaking, the large scale circulation determines the abundance of these trace species to a large extent between 10 and 100 km altitude. In the tropopause region, such mixing is often related to shear layers, i.e., regions with strong vertical changes of the wind, and ultimately to turbulence which is much less understood in the tropopause region than close to the surface.  The shear likely relates to gravity waves traveling upward and possibly breaking, however, the contribution of the gravity waves is still not clear. Additionally, the effect of small-scale motions linked to gravity waves on transporting chemical substances is still uncertain. A key gap in current numerical models is the lack of representation of how gravity waves interact with turbulence — specifically, how turbulence is generated by shear and by density changes caused by gravity waves, and how gravity waves lose energy due to friction and mixing in turbulent air. The main goal of this project is to improve the representation of gravity waves, shear, turbulence and their interactions in weather and climate models. This will be achieved through data analysis, theoretical research, development of new numerical methods, and validation against high-resolution simulations and real-world observations.

Top row: Difference (right panel) between the January-mean residual-mean streamfunction (contours) and vertical wind (colour shading, in m/s) from simulations using ICON/MS-GWaM without (left) and with (middle) horizontal GW propagation. Statistically insignificant differences are indicated by stippling. Middle row: Change in the mixing ratio (compared to a horizontally homogeneous initial state) of a passive tracer exposed to a GW packet in a fine-resolution simulation resolving the wave packet (left), and two coarse-resolution simulations either parameterising tracer fluxes using MS-GWaM (middle), or nor representing them at all (right). Bottom row: Difference (right panel) between the Jamuary-mean turbulent kinetic energy (colour shading) from simulations using ICON/MS-GWaM without (left) and with (middle) bi-directional coupling between parameterized GWs and turbulence. Top and bottom row from Banerjee et al (2025), submitted to the J. Geophys. Res., middle row from Knop et al. (2025).

Project Poster

Evaluation Poster Phase I in 2025

Members

Publications

Banerjee, T., S. Borchert, Y.-H. Kim, A. Kosareva, D. Kunkel, G. T. Masur, Z. Procházková, J. Schmidli, G. S. Voelker, and U. Achatz (2025): The Impact of Non-Orographic Gravity Waves on Transport and Mixing: Effects of Oblique Propagation and Coupling to Turbulence. [Preprint], doi: https://doi.org/10.48550/arXiv.2508.20562

Basic, I., S. Singh, and J. Schmidli (2025): Passive Tracer Evolution Under Stable Conditions: Impact of Background Wind and Valley Geometry in an Idealized Setup. Boundary-Layer Meteorology 191 (6), 1573–1472. doi: 10.1007/s10546-025-00913-0.

Jochum, F., R. Chew, F. Lott, G. S. Voelker, J. Weinkaemmerer, and U. Achatz (2025): The Impact of Transience in the Interaction between Orographic Gravity Waves and Mean Flow. Journal of the Atmospheric Sciences 82 (2), 425–442. doi: 10.1175/JAS-D-24-0158.1.

Knop, I., S. Dolaptchiev, and U. Achatz (2025): Impact of Small-Scale Gravity Waves on Tracer Transport. arXiv, [Preprint]. doi: 10.48550/arXiv.2504.01657. 

Kosareva, A., S. Dolaptchiev, P. Spichtinger, and U. Achatz (2025): A new parameterisation for homogeneous ice nucleation driven by highly variable dynamical forcings. Geoscientific Model Development 18 (18), 6117–6133. doi: 10.5194/gmd-18-6117-2025.

Quinn, B., C. Eden, D. Olbers, G. S. Voelker, and U. Achatz (2025): The Transient IDEMIX Model as a Nonorographic Gravity Wave Parameterization in an Atmospheric Circulation Model. Journal of Advances in Modeling Earth Systems 17 (5), e2023MS004121 2023MS004121, e2023MS004121. doi: 10.1029/2023MS004121

Singh, S., J. Schmidli, I. Bašták Ďurán, and S. Westerhuis (2025): Impact of the Turbulence Parameterization on Simulations of Fog Over Complex Terrain. Journal of Geophysical Research: Atmospheres 130 (13), e2024JD042610 2024JD042610, e2024JD042610. doi: 10.1029/2024JD042610

Siri Jagan, R. and J. Schmidli (2025): Impact of model resolution and turbulence scheme on the representation of mountain waves and turbulence. EGUsphere 2025, [Preprint], 1–24. doi: 10.5194/egusphere-2025-4308.

Umbarkar, M. and D. Kunkel (2025): Contribution of gravity waves to shear in the extratropical lowermost stratosphere: insights from idealized baroclinic life cycle experiments. EGUsphere 2025, [Preprint], 1–33. doi: 10.5194/egusphere-2025-351.

Achatz, U., M. J. Alexander, E. Becker, H.-Y. Chun, A. Dörnbrack, L. Holt, R. Plougonven, I. Polichtchouk, K. Sato, A. Sheshadri, C. C. Stephan, A. van Niekerk, and C. J. Wright (2024): Atmospheric Gravity Waves: Processes and Parameterization. Journal of the Atmospheric Sciences 81 (2), 237–262. https://doi.org/10.1175/JAS-D-23-0210.1

Chew, R., S. Dolaptchiev, M.-S. Wedel, and U. Achatz (2024): A Constrained Spectral Approximation of Subgrid-Scale Orography on Unstructured Grids. Journal of Advances in Modeling Earth Systems 16 (8), e2024MS004361. doi: https://doi.org/10.1029/2024MS004361

Kim, Y.-H., G. S. Voelker, G. Bölöni, G. Zängl, and U. Achatz (2024): Crucial role of obliquely propagating gravity waves in the quasi-biennial oscillation dynamics. Atmospheric Chemistry and Physics 24 (5), 3297–3308. doi: 10.5194/acp-24-3297-2024.

Listowski, C., C. C. Stephan, A. Le Pichon, A. Hauchecorne, Y.-H. Kim, U. Achatz, and G. Bölöni (2024): Stratospheric gravity waves impact on infrasound transmission losses across the International Monitoring System. Pure and Applied Geophysics, doi: 10.1007/s00024-024-03467-3.

Voelker, G. S., G. Bölöni, Y.-H. Kim, G. Zängl, and U. Achatz (2024): MS-GWaM: A 3-dimensional transient gravity wave parametrization for atmospheric models. Journal of the Atmospheric Sciences, doi: 10.1175/JAS-D-23-0153.1.

Achatz, U., Y.-H. Kim, and G. S. Voelker (Nov. 2023): Multi-scale dynamics of the interaction between waves and mean flows: From nonlinear WKB theory to gravity-wave parameterizations in weather and climate models. Journal of Mathematical Physics 64 (11), 111101. doi: 10.1063/5.016518

Chouksey, M., C. Eden, G. T. Masur, and M. Oliver (2023): A comparison of methods to balance geophysical flows. Journal of Fluid Mechanics 971, A2. doi: https://doi.org/10.1017/jfm.2023.602.

Dolaptchiev, S. I., P. Spichtinger, M. Baumgartner, and U. Achatz (2023): Interactions between gravity waves and cirrus clouds: asymptotic modeling of wave induced ice nucleation. J. Atmos. Sci., 80(12), 2861–2879. doi: https://doi.org/10.1175/JAS-D-22-0234.1.

Lachnitt, H.-C., P. Hoor, D. Kunkel, M. Bramberger, A. Dörnbrack, S. Müller, P. Reutter, A. Giez, T. Kaluza, and M. Rapp (2023): Gravity-wave-induced cross-isentropic mixing: a DEEPWAVE case study. Atmospheric Chemistry and Physics 23 (1), 355–373. doi: https://doi.org/10.5194/acp-23-355-2023.

Masur, G. T., H. Mohamad, and M. Oliver (2023): Quasi-convergence of an implementation of optimal balance by backward-forward nudging. Multiscale Modeling & Simulation 21 (2), 624–640. doi: https://doi.org/10.1137/22M1506018.

Millán, L. F., G. L. Manney, H. Boenisch, M. I. Hegglin, P. Hoor, D. Kunkel, T. Leblanc, I. Petropavlovskikh, K. Walker, K. Wargan, and A. Zahn (2023): Multi-parameter dynamical diagnostics for upper tropospheric and lower stratospheric studies. Atmospheric Measurement Techniques 16 (11), 2957–2988. doi: https://doi.org/10.5194/amt-16-2957-2023.

Weinkaemmerer, J., M. Göbel, S. Serafin, I. B. Ďurán, and J. Schmidli (2023): Boundary-layer plumes over mountainous terrain in idealized large-eddy simulations. Quarterly Journal of the Royal Meteorological Society 149 (757), 3183–3197. doi: https://doi.org/10.1002/qj.4551.

Bašták Ďurán, I., M. Sakradzija, and J. Schmidli (2022): The Two-Energies Turbulence Scheme Coupled to the Assumed PDF Method. Journal of Advances in Modeling Earth Systems 14 (5), e2021MS002922. doi: https://doi.org/10.1029/2021MS002922.

Reilly, S., I. Bašták Ďurán, A. Theethai Jacob, and J. Schmidli (2022): An Evaluation of Algebraic Turbulence Length Scale Formulations. Atmosphere 13 (4), doi: https://doi.org/10.3390/atmos13040605.

Weinkaemmerer, J., I. B. Ďurán, S. Westerhuis, and J. Schmidli (2022): Stratus over rolling terrain: Large-eddy simulation reference and sensitivity to grid spacing and numerics. Quarterly Journal of the Royal Meteorological Society 148 (749), 3528–3539. doi: https://doi.org/10.1002/qj.4372.