Untersuchung der vertikalen Kopplung durch Schwerewellen in der Marsatmosphäre
Astrophysik und Astronomie
Zusammenfassung der Projektergebnisse
The importance of small-scale gravity waves (GWs) has been well recognized in the terrestrial atmosphere, but little was known about their role in the atmosphere of Mars. This study was motivated by a few observational and theoretical evidences at the beginning, and represented the first comprehensive investigation of GWs and GW-induced processes in the middle and upper Martian atmosphere. Started as mainly theoretical and modeling, this study was greatly supported by the new observational data obtained from NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, which entered the orbit in September, 2014. First and foremost, this study revealed a continuous presence of GWs in the middle and upper Martian atmosphere. They are generated in the troposphere by various weather phenomena, transport energy and momentum upward and deposit them there, thus affecting the state and dynamics of the upper atmosphere. The study quantified amplitudes of GW disturbances in the thermosphere, their spatio-temporal distributions, and estimated the dynamical forcing (drag) that these waves impose on the global circulation and transient processes. It was found that GW drag enhances the meridional transport in the middle atmosphere (between 60 and 100 km), and greatly decelerates, and even reverses, zonal wind jets above the mesopause (approximately 100 km). Dissipating and breaking GWs induce downward heat flux that cool down the thermosphere by several tens of Kelvins. Simulations with the Max Planck Institute Mars general circulation model (MPI-MGCM) demonstrated a striking response of the mesosphere and thermosphere to dust storms in the lower atmosphere. Although the thermosphere is not directly affected by radiative effects of airborne aerosol, temperature changes there of up to 70 K have same magnitudes as in the lower atmosphere, and are mediated dynamically by GWs. A state-of-the-art spectral GW parameterization implemented in the MGCM has helped to elucidate how localized patches of cold air below the condensation threshold facilitate cloud formation, and to reproduce the observed distributions of mesospheric CO2 ice clouds. The most of remaining uncertainties with GWs, both on Earth and on Mars, are with quantifying their sources in the lower atmosphere. Because such systematic observations neither exist, nor can be expected in the near future, we performed MGCM simulations with a very high resolution in pursue of obtaining a statistical description of GW sources. Although computationally expensive, this approach revealed peculiarities of GW lifecycles (generation, propagation and obliteration), and provided means for constraining and validating GW parameterizations. This analysis lays down a foundation for a new generation of such GW schemes. A combination of the GCM modeling approach with a stream of new data from MAVEN has allowed not only for confirming many theoretical predictions, but also revealed new facts requiring explanation. The most important is that GWs are even stronger in the thermosphere than expected, and that the GW field in the upper thermosphere demonstrates a striking “universality” in the statistical sense. This study started a few years ago in a relatively underdeveloped field. Now it is becoming a mainstream with more research groups entering it, of which the growing number of scientific publications is the evidence. Fundamentally, this line of research contributes to understanding Mars’ dynamics and climate, in particular mass transport leading to escape and outgassing in the thermosphere. The long-term practical impact of the obtained results is on forecasting atmospheric drag due to GW-induced fluctuations, which may have a major effect on aerobraking operations, safety, and management of Martian spacecraft.
Projektbezogene Publikationen (Auswahl)
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Cooling of the Martian thermosphere by CO2 radiation and gravity waves: An intercomparison study with two general circulation models, J. Geophys. Res. Planets, 120, 913–927
Medvedev, A. S., F. González-Galindo, E. Yiğit, A. G. Feofilov, F. Forget, and P. Hartogh
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Internal wave coupling processes in Earth’s atmosphere, Adv. Space Res., 55, 983-1003
Yiğit, E., and A. S. Medvedev
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Comparison of the Martian thermospheric density and temperature from IUVS/MAVEN data and general circulation modeling, Geophys. Res. Lett., 43, 3095–3104
Medvedev, A. S., H. Nakagawa, C. Mockel, E. Yiğit, T. Kuroda, P. Hartogh, K. Terada, N. Terada, K. Seki, N. M. Schneider, S. K. Jain, J. S. Evans, J. I. Deighan,W. E. McClintock, D. Lo, and B. M. Jakosky
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Role of gravity waves in vertical coupling during sudden stratospheric warmings, Geosci. Lett., 3, 1-13
Yiğit, E., and A. S. Medvedev
