Noctilucent clouds (NLC) consist of ice particles that form at high altitudes above 80 km. These ice clouds occur above the polar region in the summer months due to low atmospheric temperatures down to -160°C in this height region. Observations of noctilucent clouds are of high scientific value as, provided for certain conditions, the ice particles act as tracers for air masses. High-resolution measurements of the height and brightness of noctilucent clouds therefore allow for dynamical studies in this remote region of the atmosphere. One question discussed with respect to climate change concerns the spreading of noctilucent clouds from polar to mid latitudes.
Atmospheric scientists from the DLR Institute of Atmospheric Physics (IPA) were recently successful in observing a noctilucent cloud above southern Germany using the CORAL LIDAR instrument (Link zu der Webseite Projekt CORAL) developed and built at IPA. The measurement in the night from 18 to 19 July at the Sulzberg in the Bavarian Forest shows a very thin and very bright layer of ice crystals at approximately 82 km altitude (see Figure). The temporal variations of altitude and brightness of the cloud layer are indicators for microphysical and dynamical processes happening within the cloud. The combination of atmospheric waves, changes in temperature and transport by wind makes up the structures of the cloud. Noctilucent clouds can be observed by naked eye under optimal conditions and provide for spectacular displays. In twilight, they become visible as silvery-white clouds on the northern horizon (see e.g. pictures on spaceweather.com). Visual observations date back to the year 1885.
The observation of the noctilucend cloud above the Bavarian Forest was made by a transportable LIDAR system (see picture). The instrument emits a bright green laser beam into the sky and detects the light scattered back from air molecules and aerosol particles. This type of LIDAR instrument is commonly used to measure atmospheric temperature in the altitude range 20 km to 90 km. As the about 40 nm-sized ice particles which make up noctilucent clouds cause strong backscatter, the height and brightness of these clouds can be measured with high resolution.
Contact: Dr. Natalie Kaifler