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UP: Umweltphysik
UP 22: Atmosph
äre und Klima
UP 22.2: Fachvortrag
Wednesday, March 15, 2006, 14:30–14:45, D
Observation of thin and subvisible cirrus in the tropics and mid latitudes. — •Franz Immler and Otto Schrems — Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven
Cirrus clouds were observed with a mobile Aerosol Raman Lidar (MARL) during field campaigns in the mid latitudes in 2003(Lindenberg/Germany, 53∘N, 15∘E) and in the tropics in 2004/05(Paramaribo/Suriname, 6∘N, 55∘W). Our lidar system, is capable of detecting thin cirrus including extremely thin clouds with an optical depth below 10−3. The system measures cloud altitudes with high vertical and temporal resolution and determines the depolarisation and optical depth. It can measure during day - and night-time.
In daytime cloud types including contrails are classified by means of a video camera. During the campaigns, water vapour was measured by means of balloon borne probes (Vaisala RS80/RS90, ’Snow white’ frost point hygrometer) and by the LIDAR using the Raman technique. In the mid latitudes cirrus were found in 55% of the measurements. In the tropics the cloudiness in the upper troposphere was found to be very high, since in about 90% of all measured profiles cirrus was present. Transport processes in the tropical tropopause layer were investigated with a newly developed trajectory model which is coupled with a radiative transfer model. Cloud occurrence and dehydration of the air in the model agrees well with the observations.