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We study the horizontal structure of the atmospheric gravity waves(AGW) in the height ranges between 6 and 22 km observed using theMU radar at Shigaraki in Japan, during a 3 day period in January anda 4 day period in August 1988. The data were divided by doubleFourier transformation into a data set of upward moving waves and adata set of downward moving waves for independent analysis. Thephase and group velocity tracing technique was applied to measurethe vertical group and phase velocity as well as the characteristicperiod of the gravity wave packet. Then the dispersion equation ofthe linear theory of AGW was solved to obtain its intrinsic waveperiod – horizontal wavelength and horizontal group velocity – andthe vertical flux of horizontal momentum associated with each wavepacket was estimated to help determine the direction of thecharacteristic horizontal wave vector. The results showed that thewaves with periods in the range of 30 min~6 h had horizontalscales ranging from 20 km to 1500 km, vertical scales from 4 kmto 15 km, and horizontal phase velocities from 15 m/s to 60 m/s.The upward moving wave packets of wave period of 2 h~6 h hadhorizontal group velocities mainly toward east-south-east andnortheast in winter, and mainly in the section between thedirections of west-north-west and north in summer

Statistical characteristics of AGW wave packet propagation in the lower atmosphere observed by the MU radar