First observation of one noctilucent cloud by a twin lidar in two different directions

摘要: Abstract. In the early morning hours of 14 July 1999, a noctilucent cloud (NLC) was observed simultaneously by two branches twin lidar system located at ALOMAR observatory in northern Norway (69° N). The telescopes lidars were pointing vertical (L ^ ) and off zenith 30° ). detected an enhancement altitude profile backscattered light (relative to molecular background) for more than 5 h, starting approximately 01:00 UT. These measurements constitute detection one NLC under different directions allow detailed study morphology layer. A cross-correlation analysis signals demonstrates that main structures seen both are practically identical. This implies temporal evolution microphysics within during its drift from beam other is negligible. From time delay structures, velocity 55–65 m/s derived which agrees nicely with radar wind measurements. During observation period, mean decreases ~0.5 km/h (=14 cm/s) volumes. Further-more, consistently 500 m lower L compared . Supplementing these data observations rocket-borne ground-based instruments, we show general downward progression layer through night, as lidars, caused combination particle sedimentation 4–5 cm/s directed 9–10 cm/s, whereas tilt direction can be excluded. Key words. Atmospheric composition structure (cloud physics chemistry; aerosols particles) Meteorology atmospheric dynamics (middle atmosphere dynamics)