Nestability a disipace atmosférických vnitřních gravitačních vln a jejich reprezentace v klimatických modelech.

• Thesis title in Czech: Nestability a disipace atmosférických vnitřních gravitačních vln a jejich reprezentace v klimatických modelech.
• Thesis title in English: Instabilities and dissipation of internal gravity waves in the atmosphere and their representation in chemistry-climate models.
• Key words: Vnitřní gravitační vlny|Nestabilita vlnového pole a disipace|Klimatické modely|Turbulentní promíchávání|Parametrizační schéma
• English key words: Internal Gravity Waves|Wave Instability and Dissipation|Climate Models|Turbulent mixing|Parameterization scheme
• Academic year of topic announcement: 2024/2025
• Thesis type: dissertation
• Department: Department of Atmospheric Physics (32-KFA)
• Supervisor: RNDr. Petr Šácha, Ph.D.

Guidelines

To fulfill the goals of the thesis, a summary of the known instabilities leading to GW dissipation will be reviewed together with the dissipation process and mixing efficiency under different types of instabilities. Subsequently, based on purely analytical considerations, a minimalistic theoretical model will be formulated that will connect the parameters of the wave and of the background and the type of instability with the intensity of overturning and mixing. This relationship will be tested using dedicated model simulations of the GW dissipation (with an emphasis on orographic GWs) due to different types of instabilities and under different atmospheric conditions. The results will pave the way for modifications of current GW parameterization schemes or their coupling with other sub-models to take into account the influence of wave dissipation on the transport and distribution of gaseous components in the atmosphere, thereby improving the known errors of current models and ultimately improving the quality of future climate change projections.

References

Andrews, D. G., McIntyre, M. E., Holton, J.R. and Leovy, C.B.: Middle Atmosphere Dynamics, Academic Press, London, 1987.
Fritts, David C., and M. Joan Alexander. "Gravity wave dynamics and effects in the middle atmosphere." Reviews of geophysics 41.1 (2003).
Fritts, D. C., Wang, L., Lund, T. S., Thorpe, S. A., Kjellstrand, C. B., Kaifler, B., & Kaifler, N. (2022a). Multi-Scale Kelvin-Helmholtz instability dynamics observed by PMC Turbo on 12 July 2018: 2. DNS modeling of KHI dynamics and PMC responses. Journal of Geophysical Research: Atmospheres, 127, e2021JD035834. https://doi.org/10.1029/2021JD035834
Fritts, D. C., Lund, A. C., Lund, T. S., & Yudin, V. (2022b). Impacts of limited model resolution on the representation of mountain wave and secondary gravity wave dynamics in local and global models. 1: Mountain waves in the stratosphere and mesosphere. Journal
of Geophysical Research: Atmospheres, 127, e2021JD035990. https://doi. org/10.1029/2021JD035990
Schlutow, Mark and Voelker, Georg S.. "On strongly nonlinear gravity waves in a vertically sheared atmosphere: Part I: Spectral stability of the refracted wave" Mathematics of Climate and Weather Forecasting, vol. 6, no. 1, 2020, pp. 63-74. https://doi.org/10.1515/mcwf-2020-0103
Skamarock, W. C., Snyder, C., Klemp, J. B., & Park, S. (2019). Vertical Resolution Requirements in Atmospheric Simulation, Monthly Weather Review, 147(7), 2641-2656.
Serafin, S., Rotach, M. W., Arpagaus, M., Colfescu, I., Cuxart, J., De Wekker, S. F. J., Evans, M., Grubišič, V., Kalthoff, N., Karl, T., Kirshbaum, D. J., Lehner, M., Mobbs, S., Paci, A., Palazzi, E., Raudzens Bailey, A., Schmidli, J., Wohlfahrt, G., and Zardi, D.: Multi-scale transport and exchange processes in the atmosphere over mountains, Innsbruck university press, 1 edn., https://doi.org/10.15203/99106-003-1, https://uibk.ac.at/iup/buch_pdfs/10.1520399106-003-1.pdf, 2020.

Preliminary scope of work in English

Active research during recent decades has propelled our understanding of the origin of atmospheric waves, their propagation and influence. Still, many aspects of the wave lifecycle and wave effects are to a large extent unknown and not all wave types are fully resolved or properly parameterized in state-of-the-science atmospheric models. This is particularly true for atmospheric internal gravity waves (GWs) that together with Rossby waves dominate the extratropical wave fields across the troposphere and stratosphere up to the mesopause (Andrews et al., 1987). While Rossby waves are large-scale phenomena well resolved in the models, GWs occur on a broad range of scales (from synoptic to well below mesoscale) and remain to a large extent unresolved (e.g., in chemistry-climate models (CCMs)) or are only partially resolved (i.e., lie in a grey zone in numerical weather prediction models. Hence, their effects need to be parameterized in the models, for which a complete understanding of their sourcing, propagation, stability and dissipation is needed.
In particular, our knowledge about GW instability and dissipation remains incomplete as the process inevitably includes also the turbulence and hence micro-scale processes, which makes it still a subject of active and lively theoretical research.
Currently, several instability types of the GW field are known (e.g. convective and dynamic instability, parametric-subharmonic instability, modulation instability and their combinations) and as a result, GW breaking and the turbulent transfer of momentum, energy and mixing of the surrounding layers occurs (Fritts and Alexander, 2003), often with instability sensitive characteristics. GW breaking is a strongly non-linear process, for which direct numerical simulations are increasingly used in research (Fritts et al., 2022a), but new results are still emerging even based on purely analytical considerations (Schlutow and Voelker, 2020). In current generation chemistry-climate models (CCMs), but also in numerical forecast models with detailed horizontal resolution, GW breaking is not fully resolved, and will remain unresolved in the foreseeable future (Fritts et al., 2022b).
To account for the irreversible transfer of momentum during the GW breaking, the models rely on bulk parameterizations of the resulting drag based on the linear theory. In the same time, the models employ also various forms of turbulent mixing parameterizations (Skamarock et al., 2019) that account also for the transfer of mass and energy, however, these turbulent parameterizations are by no means linked with the GW parameterizations or activity in the models. In the frame of this thesis, the applicant will improve our understanding of GW instabilities, dissipation and the induced turbulent mixing and will transfer this knowledge towards representation of these mechanism in state-of-the-science atmospheric or climate models. The topic of the thesis is perfectly aligned with the upcoming activities of the Multi-scale Transport and Exchange Processes in the Atmosphere over Mountains Programme and experiment (TEAMx; Serafin et al., 2020) that will conduct a major observational campaign in 2025. Active participation of the applicant in the campaign is expected and will be supported.