Studies of gravity wave propagation in the mesosphere observed by MU radar

摘要

Mesospheric data were analyzed by a composite method combining phase andgroup velocity tracing technique and the spectra method of Stokes parameteranalysis to obtain the propagation parameters of atmospheric gravity waves(AGW) in the height ranges between 63.6 and 99.3 km, observed using the MUradar at Shigaraki in Japan in the months of November and July in the years1986, 1988 and 1989. The data of waves with downward phase velocity and thedata of waves with upward phase velocity were independently treated. First,the vertical phase velocity and vertical group velocity as well as thecharacteristic wave period for each wave packet were obtained by phase andgroup velocity tracing technique. Then its horizontal wavelength, intrinsicwave period and horizontal group velocity were obtained by the dispersionrelation. The intrinsic frequency and azimuth of wave vector of each wavepacket were checked by Stokes parameters analysis. The results showed thatthe waves with intrinsic periods in the range30 min–4.5 hhad horizontal wavelength ranging from 25 to 240 km, vertical wavelengthfrom 2.5 to 12 km, and horizontal group velocities from 15 to 60 m s.Both upward moving wave packets and downward moving wave packets hadhorizontal group velocities mostly directed in the sector betweendirections NNE (north-north-east) and SEE in the month of November, andmostly in the sector between directions NW and SWS in the month ofJuly. Comparing with mean wind directions, the gravity waves appeared tobe more likely to propagate along with mean wind than against it. This apparent prevalence for downstream wave packets was found to becaused by a systematic filtering effect existing in the process of phase andgroup velocity tracing analysis: A significant portion of upstream wavepackets might have been Doppler shifted out of the vertical range in phaseand group velocity tracing analysis.