Monitoring the life cycle of cirrus clouds using Meteosat-4 data during ICE-1989

Abstract

During the International Cirrus Experiment (ICE), cirrus cloud properties over the North Sea were observed from local surface-based and aircraft instruments. In order to place these measurements in the context of the general space-time evolution of the cirrus systems and smaller cloud elements, Meteosat images were used to study the evolution of the clouds along their trajectories. The trajectories were established with techniques derived from those used to compute cloud motion winds from geostationary satellite images. Thermal infrared (IR) and water vapour (WV) channel tracking was performed to take advantage of the properties of each channel: better contrast of the clouds over the surface in the IR, and better discrimination of upper layers in the WV channel. Although long tracks, up to 60 hours, could be observed, they did not correspond to the same cirrus elements, or even the same system along the track. The evolution of the brightness temperatures along the tracked elements showed periodic fluctuations. The representativeness of these fluctuations in terms of cloud life cycle is discussed, as it may be related to the quality of the tracking.