By using a full-implicit-continuous-Eulerian (FICE) scheme and taking a set of basic atmospheric motion equations in spherical coordinates as governing equations, z fully nonlinear numerical model for the dynamics of the middle and upper atmosphere is established to numerically study the nonlinear global propagations and amplitude growths of large-scale gravity wave packets. The simulation results show that the newly established model can successfully exhibit the essential characteristics of the global propagations of gravity waves: wave energies propagate upward along the ray paths derived from the hnear gravity wave theory, and wave disturbance amplitudes increase with the increasing heights. During the upward propagation of gravity wave packets, there occurs evident enhancement of background wind along the propagation direction. Moreover, our simulation demonstrates that Earth rotation has little influences on the wave energy propagations and amplitude growths. However, the primary nonlinear curvature terms (uvr tan0 and -u2r tan0) play an important role in the growths of gravity wave amplitudes, which causes a evident latitudinal dependence of wave amplitude growth. In the Northern Hemisphere, with the same spatial scales and initial zonal dislurbance amplitudes, the waves propagating in lower-latitude regions have larger disturbance amplitudes.

Data obtatmed from the medlun-frequency radar at Wuhan (30°N, 114°E} from Ⅱ to 25 February and frum 28 February to 13 March have been used to study the mean wind and tidal ogcillations at mesopause (8O-98km) region over Wuhan to 13 Minter The observed zonal and meridional mean winds show obvious temporal variation and usually decrease widl the mcreasing heighls in most observational time. the zonal mean wind is eastward A Aynamic spectral analysis of disturbance amplutudc illustratcs a promincnt peak at a period of 24h al all hcighls and alines! uninterrupted, and there are occasionally shghlly stong senlldiurnal and weak lerdiurnal tidal disturbarces, indicating that in Ihe mid-lalitude regions. the diurnal tide is Ihe dominant tidal disturbance at tnesopausc in winter. The temporal variation of tidal ampbtudes and their wave kinematical cncrgies iffustrates that there may bc sigmificant resonant interaction among the diurnal, semidiurnal and terdiurnal rides A quantitative compariosn with Ihe global-scale wave model (GSWM) demonslrates that the observed diuulal and semidiurnal tidal amplitudes are less 3nd larger than lhe results of GSWM-02. respectively Tbe essentially linear GSWM carmot predicl Ihe decrease ot diurnal tidal anplitude at higher heigbts. which muy be due to several possible nonlinear processes. such at wave-Wave interaction aad wave break. Although the height vanations of tidal phases are Consistenly well with the prediction of GSWM. there are evident pbase differenees between our observation and tile model. The profiles of the diunanl tidal phases show nbvious decreasc trond with Ihe increasiong height, indicalmg the observed diurnal tide is propagating upward The vertical wavelength of Ihe observed diurnal tide is estimated to be about 37km. and die eorresponding downward phase velocity is about 15km-1h.

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

By using a two-dimensional, full-implicit-continuous-Eulerian (FICE) scheme, we simulated the nonlinear propagation and evolution of gravity wave paekels in a compressible, nonisothermal and dissipative atmosphere. The numerical results show that when an upgoing gravity wave packet is generated in the lower mesosphere, it can propagate along gs ray path until it reaches lower thermosphere. However, upon reaching the lower thennosphere, the wave packet and associated energy propagate ahnost horizontally, which departs obviously from the prediction of linear gravity wave theory under WKB approximation in the nondissipative case. Further discussion indicates that the influences of nonlinearity and background temperature are not strong enough to restrict completely the upward energy propagation of the wave packet and that the influence of constant molecular viscosity on the characteristics (energy propagation path and wave parameters) of gravity waves is insignificant. It is the vertical inhomogeneity of molecular viscosity that causes the restriction of upward energy propagation of the gravity wave packet Moreover, througheut propagation, the donlgrant vertical wavelength of the wave packet decreases with time, as it is affected by the joint actions of nonlinearity, background temperature, and dissipation. These results indicate that the molecular viscosity, especially the vertical inhomogeneity of molecular viscosity, plays an important talc in the nonlinear propagation of gravity wave packets.

Based on lidar measurements beteen March and September 2001, the charccteristics of sporadic Na layers (Na, layers) over wuhan (30.5