Horizontal variations of gravity wave activities in the lower stratosphere over Japan: A case study in the Baiu season 1991

Vertical wavenumber spectra are analyzed by using temperature, zonal wind and meridional wind data obtained with MU radar and radiosondes at the MU observatory in Shigaraki and with operational rawinsondes at five stations over Japan. The temperature and meridional wind spectral power densities of the dominant gravity wave increase with a decrease of latitude, whereas the zonal wind spectral power seems to have a maximum near the tropopausal jet stream axis. An analysis technique to estimate a characteristic value of intrinsic frequency from the wind and temperature vertical-wavenumber spectra is proposed. The different meridional distributions of spectral power densities for temperature, zonal wind and meridional wind possibly can be explained by a latitudinal distribution of the characteristic intrinsic frequency.