XeF lidar measurements of density and temperature in the middle atmosphere

In recent years, it has been widely recognized that vertically propagating internal gravity waves in the middle atmosphere play an important role in determining the large scale wind field by their momentum transport and deposition. However, very little is known about them in the upper stratosphere and lower mesosphere because of the lack of adequate techinques to observe small scale motions. A XeF excimer laser was used for the Rayleigh lidar observation. The characteristics of the XeF lidar system are given. The wavelength of the XeF laser is in the region that is ozone absorption free, and the Rayleigh scattering cross section is 5 times larger than in 532 nm. The advantages of using the XeF laser as against the YAG laser have been discussed in detail. The density and temperature profiles between the altitude range of 30 and 70 km measured with this lidar system are illustrated. The accuracy is less than + or - 3% and 10k at 60 km for an observation time of 15 min. The results on the gravity waves by the observation through about one year since Apr. 1985 is presented.