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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.
STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 In situ observations of stratospheric turbulence at sub-cm scales by new LITOS anemometer Theuerkauf Anne , Gerding Michael , Lübken Franz-Josef Leibniz Institute of Atmospheric Physics Gravity waves often dissipate at least part of their energy in the stratosphere and generate layers of turbulence. Examinations of these small scale structures are not only important for the stratosphere itself but also for the understanding of gravity wave propagation into the middle atmosphere. Stratospheric turbulence has first been measured by balloon-borne sensors more than 20 years ago. However, in-situ soundings provide the only possibility for high-resolved soundings up to 35 km altitude, but these soundings are still technically challenging and the number of soundings is sparse. We have developed a compact balloonborne payload called LITOS (Leibniz Institute Turbulence Observations in the Stratosphere). LITOS is designed for wind turbulence soundings from the ground up to 35 km altitude by use of a constant-temperature anemometer (CTA, also called hot-wire anemometer). For the first time a vertical resolution of ~2.5 mm is achieved for stratospheric soundings. The balloon payload has been launched several times since autumn 2007 from our site at Leibniz- Institute of Atmospheric Physics (IAP) at Kühlungsborn, Germany (54°N, 12°E). Two additional soundings are carried out in 2008 and 2009 at Kiruna, Sweden (67°N, 12°E) as part of the BEXUS program. We observed thin turbulent layers of 20-100 m thickness, partly up to 500 m in a mainly non-turbulent atmosphere. Power spectral densities of vertical wavenumbers reveal slopes of m -5/3 and m -7 , indicative of the inertial and viscous subrange. Energy dissipation rates are determined from the best fit of a theoretical model to the measured spectrum. Within the turbulent layers dissipation rates strongly vary between 0.05 mW/kg (weak turbulence) and 20 mW/kg (strong turbulence). These energy dissipation rates deviate by a maximum factor of 100 from earlier indirect measurements. We will show examples of turbulent layers and the corresponding altitude-resolved energy dissipation rates. We will discuss the occurrence of these turbulent layers and their relation to atmospheric background parameters as observed simultaneously by radar, lidar and radiosondes
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scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

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