Planetary scale and tidal perturbations in mesospheric temperatures observed by WINDII

Quasi two-day wave (QTDW) and semidiurnal tides are important dynamical features in the mesosphere and lower thermosphere region. The objective of this research is to study the dynamical structure and the latitudinal and seasonal variations of these waves. Mesospheric (65 to 90 km altitude) temperatures derived from the Rayleigh scattered sunlight measurements from the background filter centered at 553 nm wavelength are employed in this study. The measurements are made by the Wind Imaging Interferometer (WINDII) aboard the Upper Atmosphere Research Satellite (UARS). The analysis is accomplished by comparing WINDII observations during July 92, March/April/December 92/93 and January 93/94 to results of previous observations and model simulations.; The observational data are first grouped into 10-degree latitude bins and interpolated into 1 km altitude bins. Spectral analysis is employed to resolve a 2-dimensional (2D) space-time spectrum by fitting the observations into traditional wave functions in a Least-Mean-Squares sense. The coefficients for a wave with frequency sigma (day-1) and wavenumber s give the amplitude and phase of this wave, while the chi 2 value is the goodness-of-fit index to search for significant wave components in a given data set.; A strong January QTDW with a maximum amplitude of 15 K at 20°S at 83 km height, and a weaker July QTDW were identified and found to be in good agreement with QTDW temperature results from the Microwave Limb Sounder observations (Wu et al., 1996). While July's QTDW is subject to strong influence from tides and a 2-day/wavenumber-4 wave, a 2-day/wavenumber-3 wave dominates the January QTDW. It is shown that the sampling is crucial in retrieving semidiurnal tidal information. WINDII spring semidiurnal observations differ from some model predictions. The results are discussed in detail and future topics of investigation are outlined.