Analysis of the equatorial semiannual oscillation and quasi two-day wave in the mesosphere and lower thermosphere using a spectral model and data collected with the Christmas Island radar systems

A VHF wind profiling radar was installed at Christmas Island, which is located in the equatorial Pacific, during 1988. The installation of the wind profiler and a meteor echo detection and collection system has provided us with observations of the horizontal wind field in the troposphere and in the lower thermosphere. Analysis of the lower thermospheric horizontal wind field provides evidence of an equatorial semiannual oscillation and quasi two-day wave. The semiannual oscillation observed in the lower thermospheric zonal wind field is in qualitative agreement with rocket and satellite observations.; The quasi two-day wave observed in the Christmas Island lower thermospheric data is a dominant feature of the meridional wind field in late January. Analysis of the quasi two-day wave during late January indicates a wave period near 48 hours and a variable vertical wavelength. Additionally, analysis of the tropospheric data was performed and does not indicate the presence of the quasi two-day wave in the lower atmosphere. Using the zonal mean winds estimated from the tropospheric and lower thermospheric data, a set of numerical experiments were performed with a linearized spectral model. The results of these experiments indicate the resonant response and global amplitude structure of the quasi two-day wave is sensitive to variations in the mean zonal wind field.