First observation of one noctilucent cloud by a twin lidar in two different directions
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<font face="Symbol"...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2002-11-01
|
| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/20/1863/2002/angeo-20-1863-2002.pdf |
| Summary: | 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<font face="Symbol" ><sub>^</sub></font>) and off the zenith
by 30° (L<sub>30°</sub>). 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<sub>30°</sub>
compared to L<font face="Symbol" ><sub>^</sub></font>. 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.<br><br><b>Key words. </b>Atmospheric composition and structure
(cloud physics and chemistry; aerosols and particles) Meteorology and
atmospheric dynamics (middle atmosphere dynamics) |
|---|---|
| ISSN: | 0992-7689 1432-0576 |