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

• Main Authors: Baumgarten, G., Lübken, F.-J., Fricke, K. H.
• Other Authors: Leibniz-Institut für Atmosphärenphysik (IAP), Universität Rostock-Leibniz Association, Physikalisches Institut Bonn, Rheinische Friedrich-Wilhelms-Universität Bonn
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2002
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Norway; Alomar; Northern Norway
• Online Access: https://hal.archives-ouvertes.fr/hal-00317402; https://hal.archives-ouvertes.fr/hal-00317402/document; https://hal.archives-ouvertes.fr/hal-00317402/file/angeo-20-1863-2002.pdf

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