Dynamics of the Mesosphere and Lower Thermosphere as Seen by MF Radars and by Hrdi/uars
Abstract
The High Resolution Doppler Imager (HRDI) instrument on-board the Upper Atmosphere Research Satellite (UARS) measures global winds in the mesosphere and lower thermosphere on a day-to-day basis. This offers a unique opportunity to obtain global scale dynamical information in this region of the atmosphere. In this study, the HRDI wind data are presented and compared with Medium Frequency (MF) radar data. It is found that in the upper mesosphere, the tidal amplitudes obtained by HRDI can be bigger than those from MF radars by a factor of two. The analysis suggests that MF radars systematically underestimate wind magnitudes in the upper mesosphere, especially above 90 km. Scarce sampling pattern of HRDI measurements makes conventional methods of tidal analysis (Fourier analysis, least squares fitting) cumbersome. An original method of analysis based on a numerical model of atmospheric thermal tides is proposed and applied to the HRDI data. This technique is used to derive monthly mean altitude-latitude cross -sections of the amplitudes and phases of the tidal perturbations of zonal, meridional, and vertical velocity, pressure, temperature, and the dissipation from two years (1992-1993) of HRDI observations. The results show profound seasonal changes in the derived tidal amplitudes and dissipation. These changes are consistent with what is known from the gravity wave breaking theory. It is shown that tides and the dissipation derived from the HRDI observations reach their maxima approximately 5-10 km higher than what is seen from MF radar data and from theoretical calculations by Garcia and Solomon (1985).
- Publication:
-
Ph.D. Thesis
- Pub Date:
- January 1995
- Bibcode:
- 1995PhDT.......125K
- Keywords:
-
- WIND;
- TIDAL AMPLITUDE;
- Physics: Atmospheric Science