A simple method to derive Fourier-wavelet spectra for studying global-scale waves in the mesosphere and lower thermosphere region

Global-scale waves, such as tides and traveling planetary waves, are an important part of the meteorology of the mesosphere and lower thermosphere (MLT) region. The amplitude and phase of these waves can be determined by analyzing longitude-time data given at a certain height and latitude. The standard technique is the least-squares Fourier method. However, it has difficulties in resolving the temporal variability of the wave activity. Tides and traveling planetary waves are known to show considerable temporal variability in the MLT region. In this presentation, a simple method to derive Fourier-wavelet spectra, which can resolve temporal variability of wave activity, is introduced. The technique enables to obtain a 'wavelet-like' spectrum, separately for eastward- and westward-propagating global-scale waves with different zonal wavenumbers. Application examples are presented using data from whole atmsophere models. The results suggest that the technique is capable of capturing bursts of global-scale wave activity in the MLT region during sudden stratospheric warming events.