NOCTILUCENT CLOUD OBSERVATIONS OVER GREENLAND BY A RAYLEIGH LIDAR

We report on the detection of noctilucent clouds (NLCs) by a Rayleigh lidar system located on the west coast of Greenland during operations in July and August 1994. The lidar detected NLCs in the zenith on thre e nights (July 28-29, July 31-August 1, and August 4). The lidar measu rements are presented at temporal(1 minute) and spatial (192 meter) re solutions exceeding previously reported lidar measurements of NLCs and reveal significantly more structure in the clouds. Unique cloud featu res are observed for each night NLCs were detected. Because of the lar ge backscatter ratio associated with NLCs, the volume backscatter coef ficient for the cloud particles can be determined more accurately from the lidar signal than the backscatter ratio as the upper mesospheric molecular number density is negligible in the volume backscatter coeff icient calculation. The volume backscatter coefficient values determin ed from the three nights of NLC observations would be classified by cu rrent models as moderate to extreme. The extreme backscatter from NLC measurements on August 4 tests the assumptions used in existing models .