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Publications within Project GWING

  • Stephan, C. C., Schmidt, H., Zuelicke, C., & Matthias, V. (2020). Oblique gravity wave propagation during sudden stratospheric warmings. Journal of Geophysical Research: Atmospheres, 125, e2019JD031528. https://doi.org/10.1029/2019JD031528
  • 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
  • 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
  • S. Borchert, G. Zhou, M. Baldauf, H. Schmidt, G. Zängl and D. Reinert. The upper-atmosphere extension of the ICON general circulation model (version: ua-icon-1.0). Geosci. Model Dev., 12, 3541-3569, https://doi.org/10.5194/gmd-12-3541-2019, 2019

 

 

Abstracts:

Oblique Gravity Wave Propagation During Sudden Stratospheric Warmings: Stephan, C. C., Schmidt, H., Zuelicke, C., & Matthias, V, Journal of Geophysical Research

Gravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper‐atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal‐mean stratospheric warming is accompanied by zonal‐mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s urn:x-wiley:jgrd:media:jgrd55943:jgrd55943-math-0001) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle‐atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies.

The upper-atmosphere extension of the ICON general circulation model: S. Borchert, G. Zhou, M. Baldauf, H. Schmidt, G. Zängl and D. Reinert; Geosci. Model Dev., 12, 3541-3569, 2019

How the upper-atmosphere branch of the circulation contributes to and interacts with the circulation of the middle and lower atmosphere is a research area with many open questions. Inertia–gravity waves, for instance, have moved in the focus of research as they are suspected to be key features in driving and shaping the circulation. Numerical atmospheric models are an important pillar for this research. We use the ICOsahedral Non-hydrostatic (ICON) general circulation model, which is a joint development of the Max Planck Institute for Meteorology (MPI-M) and the German Weather Service (DWD), and provides, e.g., local mass conservation, a flexible grid nesting option, and a non-hydrostatic dynamical core formulated on an icosahedral–triangular grid. We extended ICON to the upper atmosphere and present here the two main components of this new configuration named UA-ICON: an extension of the dynamical core from shallow- to deep-atmosphere dynamics and the implementation of an upper-atmosphere physics package. A series of idealized test cases and climatological simulations is performed in order to evaluate the upper-atmosphere extension of ICON.

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.

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., accepted, 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.