Atmospheric coupling by gravity waves:climatology of gravity wave activity, mesopheric turbulence and their relations to solar activity

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Gravity waves are very important for the coupling between different regions of the middle atmosphere. They are normally created in the troposphere, are filtered by the wind field in the strato- and lower mesosphere and dissipate at least partly in the upper mesosphere and lower thermosphere. The transfer of momentum and energy creates a residual circulation which is responsible for the strong deviations of the temperature and wind field in the MLT region from radiative equilibrium. In this proposal, investigations are done to study the activity of gravity waves, their filtering by the mean circulation and the deposition of momentum and heat. The data base comprises time series of mesospheric wind measurements, partly available since 1990, and turbulent energy dissipation rates estimated from spectral width measurements with a narrow beam Doppler MF radar. At moderate solar activity (2005-2008) an extensive data base covering high, middle, and low latitudes on both hemispheres is available in the frame of the CAWSES Global Tidal Study. Furthermore, the variability of mesospheric temperatures is derived from continuous radar observations of meteor decay times. Vertical coupling by gravity waves and planetary waves as well as wave interaction are investigated in detail during stratospheric warming events. The influence of solar activity on the dynamical and thermal state of the mesosphere is studied on the basis of long-term measurements of wind and temperature variances. Particular attention is devoted to the response of the mesospheric wind field, turbulence, and temperature of the mesopause region on solar activity storms. The observed activity of gravity waves and their dissipation in the mesosphere and lower thermosphere will be compared with the results obtained by general circulation models.