scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Noctilucent cloud observations at mid-latitudes by lidar: mean state, variability, and
relation to ambient conditions of temperatures and winds
Gerding Michael , Höffner Josef , Kopp Maren , Hoffmann Peter , Zecha Marius , Lübken Franz-Josef
Leibniz Institute of Atmospheric Physics
Temperatures in the polar summer mesopause region are low enough to form ice particles
known as Noctilucent Clouds (NLC) or Polar Mesospheric Clouds (PMC). With decreasing
latitude NLC occurrence is generally decreasing due to rising temperatures. Southward of
60°N average temperatures are near or even higher than the frost point temperature and NLC
are only rarely observed. Therefore NLC occurrence is expected to change strongly with only
minor variations in temperature and water vapour, i.e. it depends strongly on atmospheric
waves, trends, and the solar cycle. Since 1997 NLC are observed at Leibniz Institute of
Atmospheric Physics at Kühlungsborn, Germany (54°N, 12°E) during night by lidar at 532
nm wavelength. The altitude distribution centres at 82.9 km, i.e. similar to the polar NLC
distribution even if the temperature structures are quite different at both latitudes. On average,
the probability for NLC observations at 54°N is largest around day 180, which is about 10
days after the temperature minimum in the mesopause region. The NLC occurrence rate
shows a strong interannual variation with a minimum in the early 2000s (roughly 0 %) and the
highest rate near 20 % in 2009. The variation suggests a relation with the solar activity, but
this mechanism does not explain the high variability observed between 2005 and 2009. We
will compare the NLC occurrence rate to average temperatures and winds observed at out site
by lidar and radar. During summer 2009 we have performed first observations with a daylight
capable lidar at 532 nm, measuring NLC independent of solar elevation. By this the retrieval
of diurnal variations of NLC occurrence and strength will be possible at our mid-latitude site,
being one of very few stations in the world. Simultaneous observations of NLC and
Mesospheric Summer Echoes (MSE) are limited to daytime since electron densities have to be
sufficiently high. The new capabilities of the RMR lidar at Kühlungsborn together with the
co-located OSWIN VHF radar and the K lidar allow first case studies from simultaneous NLC
and MSE observations at mid-latitudes.