Proceedings with Extended Abstracts (single PDF file) - Radio ...

latitudinal dependence of the seasonal variation of the wave activity similar to that observedhere has been reported earlier [e.g., Fritts and vanZandt, 1993].The wavenumber-power spectra for the same days as of the frequency spectra arepresented in figures 3(a) and 3(b). The dominant components have vertical wavelengths inthe range of about 5-20 km. The most dominant component with a wavelength of about20 km is observed during the day of autumn equinox. From the figure (1) and (2), it isFigure 2. Frequency– Power spectra of relative temperature fluctuation as function of height for the casesshown in figure 1.evident that the modes with vertical wavelengths greater than 5 km correspond to longerperiod waves (> 4 ½ hrs). These modes with low rate of vertical phase propagation are seenclearly at stratospheric heights and were referred to as quasi-stationary modes [Wilson et al.,1990]. The basic characteristics of these modes are found to be similar to that observed overmidlatitudes [Gardner et al., 1989; Wilson et al., 1990; Beatty et al., 1992]. The differencenoted in the seasonal dependence between the larger and shorter period modes need to beconfirmed with a larger database than used here.Figure 3. Wavenumber – Power spectra for the 64 vertical profiles of relative temperature fluctuation for thecases shown in figure 1.243