Vnitřní gravitační vlny a polární vír ve stratosféře

• Název práce v češtině: Vnitřní gravitační vlny a polární vír ve stratosféře
• Název v anglickém jazyce: Internal Gravity Waves and the Stratospheric Polar Vortex
• Klíčová slova: Vnitřní gravitační vlny|Rossbyho vlny|Stratosféra|Polární vír
• Klíčová slova anglicky: Internal Gravity Waves|Rossby Waves|The Stratosphere|Polar Vortex
• Akademický rok vypsání: 2024/2025
• Typ práce: disertační práce
• Ústav: Katedra fyziky atmosféry (32-KFA)
• Vedoucí / školitel: prof. RNDr. Petr Pišoft, Ph.D.

Zásady pro vypracování

The applicant will choose suitable high-resolution and apply traditional as well as the most recent methods for the polar vortex state diagnostics. Further, polar vortex and resolved gravity waves (GWs) will be diagnosed using state-of-the-science techniques and dynamical analysis using traditional as well as novel theoretical frameworks. Subsequently, composite analyses with regard to the GW activity and the type of Sudden Stratospheric Warming (SSW) will be produced for all of the pre-processed quantities and also interesting SSW events will be selected and analysed in detail. Particular focus in the analyses will be on the possible role of GWs for SSWs and whether resolved GWs can influence the stratospheric polar vortices as efficiently as parameterized GW drag in chemistry-climate models, through modifying the propagation of leading planetary wave modes. This information will be then transferred towards development of modified GW parameterization schemes.

Seznam odborné literatury

Alexander, M.J.: Gravity Waves in the Stratosphere. In The Stratosphere: Dynamics, Transport, and Chemistry (eds L.M. Polvani, A.H. Sobel and D.W. Waugh), 2010.
Baldwin, M. P., Ayarzagüena, B., Birner, T., Butchart, N., Butler, A. H., Charlton‐Perez, A. J., ... & Pedatella, N. M. (2021). Sudden stratospheric warmings. Reviews of Geophysics, 59(1), e2020RG000708.
Butler, A. H., Sjoberg, J. P., Seidel, D. J., & Rosenlof, K. H. (2017). A sudden stratospheric warming compendium. Earth System Science Data, 9(1), 63-76.
Hall, R. J., Mitchell, D. M., Seviour, W. J. M., & Wright, C. J. (2022). How Well Are Sudden Stratospheric Warming Surface Impacts Captured in CMIP6 Climate Models?. Journal of Geophysical Research: Atmospheres, 127(7), e2021JD035725.
Harvey, V. L., Datta‐Barua, S., Pedatella, N. M., Wang, N., Randall, C. E., Siskind, D. E., & van Caspel, W. E. (2021). Transport of nitric oxide via Lagrangian coherent structures into the top of the polar vortex. Journal of Geophysical Research: Atmospheres, 126(11), e2020JD034523.
Hitchcock, P., & Simpson, I. R. (2014). The downward influence of stratospheric sudden warmings. Journal of the Atmospheric Sciences, 71(10), 3856-3876.
Pedatella, N. M., & Harvey, V. L. (2022). Impact of strong and weak stratospheric polar vortices on the mesosphere and lower thermosphere. Geophysical Research Letters, 49(10), e2022GL098877.
Rao, J., Garfinkel, C. I., & White, I. P. (2020). Predicting the downward and surface influence of the February 2018 and January 2019 sudden stratospheric warming events in subseasonal to seasonal (S2S) models. Journal of Geophysical Research: Atmospheres, 125, e2019JD031919.
Richter, J. H., Sassi, F., & Garcia, R. R., (2010). Toward a Physically Based Gravity Wave Source Parameterization in a General Circulation Model, Journal of the Atmospheric Sciences, 67(1), 136-156.
Šácha, P., Lilienthal, F., Jacobi, C., and Pišoft, P., (2016). Influence of the spatial distribution of gravity wave activity on the middle atmospheric dynamics, Atmos. Chem. Phys., 16, 15755-15775.
Šácha, P., Kuchar, A., Eichinger, R., Pisoft, P., Jacobi, C., & Rieder, H. E.. Diverse dynamical response to orographic gravity wave drag hotspots — a zonal mean perspective. Geophysical Research Letters, 48, e2021GL093305. https://doi.org/10.1029/2021GL093305, 2021.
Vignon, E., & Mitchell, D. M. (2015). The stratopause evolution during different types of sudden stratospheric warming event. Climate Dynamics, 44, 3323-3337.

Předběžná náplň práce v anglickém jazyce

The horizontal circulation in the extratropical stratosphere and lower mesosphere during the hemispheric winter is characterized by strong westerly winds encircling a low-pressure and cold center over the pole. Its formation/fading is directly related to the cooling/heating of the pole due radiative or adiabatic effects. The variability of the vortex is mostly due to Rossby and gravity waves propagating vertically from the troposphere leading to a weakening of the vortex and possible mixing of air through through the polar vortex boundary that otherwise acts as a barrier. In the most extreme cases (occurring in two-thirds of the winters), the vortex is split or displaced from the pole, and the temperature rises for several days, one of the most dynamical atmospheric phenomenon called Sudden Stratospheric Warming (SSW). See (Baldwin et al., 2021) and (Butler et al.,2017) for more information on polar vortices and SSWs in both hemispheres. SSWs influence the stratosphere and troposphere including the weather at the surface (Hitchcock and Simpson, 2014), but also the mesosphere and lower thermosphere (MLT) (Vignon and Mitchell, 2015). In the stratosphere and above, the primary impact of SSWs is on temperature distribution and zonal circulation, which affects the Brewer-Dobson circulation, and thus the transport and distribution of chemical elements with a significant impact on atmospheric tides (Pedatella and Harvey, 2022). At the same time, changes in the background wind conditions are accompanied by changes in the propagation of Rossby and gravity waves (GWs) influencing the coupling between atmospheric layers. Current generation global circulation and chemistry-climate models (CCMs) have a well-known bias in simulating the frequency and type of SSWs (Hall et al., 2022) and the recent research suggests that the unintended effects of GW parameterizations can be an important cause to it (Šácha et al., 2016).
GW parameterizations supplement the transfer of momentum from the sub-grid scale orography (OGW parameterizations) or other than orographic sources (convection, fronts etc.; nOGW parameterizations). OGW parameterizations have originally been applied to separate the stratospheric polar night jet from the tropospheric subtropical jet by reducing its overall magnitude and increasing the easterly wind shear in the upper troposphere (see Alexander et al., 2010). The nOGW schemes improved simulations of the upper levels of the middle atmosphere and drove more realistic quasi-biennial and mesospheric semiannual oscillations (Richter et al., 2010). However, recent research indicated that particularly the OGW parameterizations have several effects on dynamics and transport in the models that are not constrained from observations and can be possibly artificial (Šácha et al., 2021). This uncertainty together with the increasing availability of GW resolving datasets, presents an excellent and timely motivation for the thesis. The over-arching goal of the thesis will be to test the ability of high-resolution models to simulate the SSWs and re-examine the impact of GWs on their frequency and type. Ultimately, this knowledge will be translated to the development of modified GW parameterizations resulting in improvements of the SSW representation in CCMs and the alleviation of uncertainty of future climate projections.