| In the first part of this thesis, the observational evidence of gravity-wave interactions with the two-day wave and stratospheric sudden warming events are described. The United Kingdom Meteorological Office Reanalysis data is used to obtain the tropospheric and stratospheric background wind and the Medium Frequency radar data from Urbana, EL is used to obtain the mesospheric background wind and gravity-wave activity. In the case of the two-day wave, observed meridional gravity-wave interaction signature at 93 km mimics the periodicity of the observed two-day modulation in the background meridional wind at 84 km, but the gravity-wave modulation is anti-correlated. For the stratospheric sudden warming, the zonal gravity-wave interaction signature at 69 km is positively correlated with the back-ground zonal wind modulation at 55 km.; These observed interaction signatures are then compared to the interaction signatures predicted by three commonly used gravity-wave parameterizations: critical level filtering, linear saturation filtering, and diffusive filtering. A one-dimensional, time-independent model filters various gravity-wave spectra using the criteria for each of these parameterizations. Background wind profiles for different times during the large-scale flow event are used to obtain filtered gravity-wave activity signatures that vary over time. In order to reproduce the observed interaction signature for both large-scale flow events, a broad spectrum released at 55 km was needed. These model results would indicate that the gravity waves that reach the mesosphere do not propagate from the troposphere, but are generated more locally. |
