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The Purple Crow Lidar (PCL) is a large power-aperture product monostaticRayleigh-Raman-Sodium-resonance-fluorescence lidar, which has been inoperation at the Delaware Observatory (42.9° N, 81.4° W, 237 melevation) near the campus of The University of Western Ontario since 1992.Kinetic-energy density has been calculated from the Rayleigh-scatter systemmeasurements of density fluctuations at temporal-spatial scales relevant forgravity waves, e.g. soundings at 288 m height resolution and 9 min temporalresolution in the upper stratosphere and mesosphere. The seasonal averagesfrom 10 years of measurements show in all seasons some loss of gravity-waveenergy in the upper stratosphere. During the equinox periods and summer themeasurements are consistent with gravity waves growing in height with littlesaturation, in agreement with the classic picture of the variations in theheight at which gravity waves break given by Lindzen (1981). The mean valuescompare favourably to previous measurements when computed as nightlyaverages, but the high temporal-spatial resolution measurements showconsiderable day-to-day variability. The variability over a night is oftenextremely large, with typical RMS fluctuations of 50 to 100% at allheights and seasons common. These measurements imply that using a daily ornightly-averaged gravity-wave energy density in numerical models may behighly unrealistic

Seasonal and nightly variations of gravity-wave energy density in the middle atmosphere measured by the Purple Crow Lidar