Observations with the SOUSV VHF Radar in the mesolpause region during summer 1989 show lay- ers of strong echo ictensity and wind speeds increasing with height. Occasionally, quasi-manochromatic internal gravity waves occur in the bottom side of the echo layer and vanish in the height intervaI around the echo intensity maximum which tends to increase withh increasing wave amplitude The data anaiysis can be performed using a Boussieesq and a WKB approximation, It shows that the horizontal phase trace velocity of the observed gravity waves is equal to the background wind velocity at the height of the echo intensity maximum. The observations thus reprsent nonlinear gravity wave-critical level encounters pruducing strong turbulence in the neutral gas. But the, estimated euergy disspation rates are too small to produce neutral gas turbulence at scales equal to haft the radar wave!ength yieiding an additional indication for yet unidentified mechanism generating small-scale structure in the electron gas.

By amdyzing tile resutts of the numerical sinlulations ol nonlinear propagation of three Gaussian gravlly-wave packms in isothermal atmosphere individually, tile nonlinear effects on the characteristics of glavity waves are studied quantitatively. The analyses show that during the nonlinear propagation of gravity wave packets the mean fows are accelerated and the vertical wavelengths show clear reduction due to non-linearity 011 the other band, though nonlinear effects exist, the time variations of the fi'equencies of gravity wuve packets are close to those derived from the dispersion relation and the amplitude and phase relations of wave-associated disturbance components are consistent with the pledictions of the polarization rchttion of giavity waves. This indicates that the dispersion and polarization rehltions based on the linear grawty wave theory can be applied extensively in the nonlinear region

Here is die first report on the observation of meteor ablation trails with tidar in China. Four long-lived Na ablation trails were el)served during the 18/19 Nov, 2001 Leonid meteor shower with a sodium resunance lidar over Wuhan. The Mean altitude of the 4 trails is 97.95kin. coaststeal with Leonid high entry velocity (-72kn/s). The peak deusit) averages about 3380

Data obtained from the mobile SOUSY VHF rodar at Andoya/Norway (69