Multiannual observation of noctilucent clouds above ALOMAR

Details Multiannual observation of noctilucent clouds above ALOMAR Multiannual observation of noctilucent clouds above ALOMAR

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsa22a..06b&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SA22A-06

Physics

0305 Aerosols And Particles (0345, 4801, 4906), 0320 Cloud Physics And Chemistry, 0340 Middle Atmosphere: Composition And Chemistry

Scientific paper

We report on observations of noctilucent clouds (NLC) using the ALOMAR Rayleigh/Mie/Raman (RMR) lidar in Northern Norway at 69N from 1997 to 2005. At this latitude NLC occur regularly from the beginning of June to the middle of August. Using the primary wavelength of the lidar at 532 nm we have observed NLC signatures covering all local times even during highest solar background conditions. We use the vertically resolved volume backscatter coefficient (VBC) of the NLC particles to determine cloud brightness, altitude, and vertical extension. The year-to-year variation of the NLC occurrence, the ratio of NLC to total measurement time, shows for bright clouds a modulation by solar activity while weak clouds steadily reoccur. Investigations of the local time dependencies of cloud occurrence, brightness, and altitude yield a remarkable persistence concerning diurnal and semidiurnal variations, which allows to conclude that NLC above ALOMAR are significantly affected by atmospheric tides in temperature and/or wind. For bright cloud events, we extend our observations by using the backscatter from NLC particles at all three wavelengths emitted by the lidar. The wavelengths are widely separated, from the infrared (1064 nm) over the visible (532 nm) into the ultraviolet (355 nm) spectral range, which allows to study the sizes of the NLC particles. Presuming that the particles consist of ice, we are able to derive the three parameters number density, median radius and width describing the size distribution. We discuss the observations during the recent 9 summers with respect to the water vapour needed to form noctilucent clouds and with the meteor flux measured by the SkiYMET radar located at ALOMAR.

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