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UP: Fachverband Umweltphysik

UP 1: Atmosphäre und Klima I

UP 1.4: Vortrag

Montag, 26. März 2007, 10:15–10:30, H48

Cirrus and dehydration at the tropical tropopause — •Franz Immler¹, Kirstin Krüger², Masatomo Fujiwara³, and Otto Schrems¹ — ¹Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven, Deutschland — ²IFM-GEOMAR, Kiel, Deutschland — ³Hokkaido University, Saporro, Japan

Thin ice clouds were frequently observed in the tropical tropopause layer (TTL) around 17 km altitude with our mobile aerosol Raman lidar instruments during our recent ground-based (Paramaribo, Suriname, 6°N, 55°W) and ship-borne (RV Polarstern) measurement campaigns. In the tropics, the cloudiness in the upper troposphere was found to be very high, since cirrus was present in more than 80% of all our measured profiles. Transport processes in the TTL were investigated with a newly developed trajectory model which is coupled with a radiative transfer model. This analysis suggests that clouds are always present in the TTL where the air is saturated with respect to ice due to adiabatic cooling. Also, we find evidence, that thin cirrus efficiently dehydrate ascending air. The temperature in the TTL is strongly influenced by downward propagating equatorial Kelvin waves. We find a strong correlation between the phase of the waves and the occurrence of cirrus. Extremely thin layers of solid particles which occur frequently at the cold point tropopause seem to be rather composed of NAT than of pure water ice.