Influence of internal gravity waves on the thermosphere above the turbopause
Final Report Abstract
The turbopause is an imaginary layer that separates two dynamically different atmospheric regions. They are the lower and middle atmosphere, dominated by waves and geophysical turbulence of various scales, and the viscous upper atmosphere. Molecular diffusion exponentially increases with height synchronously with the decreasing density, and severely damps and smears atmospheric eddies. The role of these eddies in the middle atmosphere dynamics, especially of small-scale internal gravity waves (GWs), has been widely recognized over the last three decades. Generated in the troposphere by meteorological motions and convection, these waves propagate upward, transport momentum, heat and energy, and deposit them in the middle atmosphere upon breaking and dissipation. However, it was thought that the majority of GWs are destroyed in the middle atmosphere, and their influence on the thermosphere is insignificant and negligible. One the other hand, observations presented numerous examples of GW packets in the thermosphere, whose origin could be traced back to sources in the troposphere. We found a theoretical way of self-consistently accounting for all major dissipative processes that affect internal waves in the entire atmosphere, and of estimating the effects they produce on the circulation. It consists of the state-of-the-art extended spectral parameterization of gravity waves interactively coupled with a "whole atmosphere" general circulation model (GCM). Over the course of the DFG project, we systematically studied effects produced by GWs of lower atmospheric origin in Earth’s thermosphere using the Coupled Middle Atmosphere-Thermosphere-2 (CMAT2) GCM. It was found that the influence of these waves on the thermosphere, which was never accounted for before, is enormous. In particular, GWs produce acceleration and (mainly) deceleration of the mean flow with the magnitude of hundreds, and even thousands, of m s-1 day-1, especially in the polar regions. Taking it into account, we were able to reproduce for the first time many observational features. Heating produced by GWs turned out to be comparable with the major heating mechanism in the thermosphere - the Joule heating, while GW-induced cooling rates can be up to a half of those produced by the main cooling mechanism in the thermosphere - molecular heat conduction. We investigated the dependence of GW effects on the solar activity, peculiarities of the wave propagation during sudden stratospheric warmings, the GW imprint on the small-scale thermospheric variability. The results of this study have allowed to appreciate the tropospheric influence on the upper atmosphere, and improve the corresponding modeling and predicting tools. The methods and approaches developed at this study are now actively applied to studying the vertical coupling in other planetary atmospheres, in particular with our Martian GCM (MAOAM).
Publications
- Definition of a generalized diabatic circulation based on a variational approach. Izv. Atmos. Ocean. Phys., 43:436–441, 2007
A. S. Medvedev
- Parameterization of the effects of vertically propagating gravity waves for thermosphere general circulation models: Sensitivity study. J. Geophys. Res., 113, 2008
E. Yiğit, A. D. Aylward, and A. S. Medvedev
- Heating and cooling of the thermosphere by internal gravity waves. Geophys. Res. Lett., 36, 2009
E. Yiğit and A. S. Medvedev
- Modeling the effects of gravity wave momentum deposition on the general circulation above the turbopause. J. Geophys. Res., 114, 2009
E. Yiğit, A. S. Medvedev, A. D. Aylward, P. Hartogh, and M. J. Harris
- Internal gravity waves in the thermosphere during low and high solar activity: Simulation study. J. Geophys. Res., 115, 2010
E. Yiğit and A. S. Medvedev
- Estimates of gravity wave drag on mars: indication of a possible lower thermospheric wind reversal. Icarus, 211:909–912, 2011
A. S. Medvedev, E. Yiğit, and P. Hartogh
- Influence of gravity waves on the martian atmosphere: General circulation modeling. J. Geophys. Res., 116, 2011
A. S. Medvedev, E. Yiğit, P. Hartogh, and E. Becker
- Dynamical effects of internal gravity waves in the equinoctial thermosphere. J. Atmos. Solar-Terr. Phys., 2012
E. Yiğit, A. S. Medvedev, A. D. Aylward, J. Ridley, M. J. Harris, M. B. Moldwin, and P. Hartogh
- Gravity waves in the thermosphere during a sudden stratospheric warming. Geophys. Res. Lett., 39, 2012
E. Yiğit and A. S. Medvedev
(See online at https://doi.org/10.1029/2012GL053812) - Thermal effects of internal gravity waves in the Martian upper atmosphere. Geophys. Res. Lett., 2012
A. S. Medvedev and E. Yiğit
(See online at https://doi.org/10.1029/2012GL050852)
