A detection method for cirrus clouds using CRISTA 1 and 2 measurements Original Research Article

During both missions of the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument in November 1994 and August 1997 high reaching tropical clouds at and above the tropopause could be observed. For the cloud detection a simple but effective cloud indicator was developed and tested under different extreme atmospheric conditions. Estimated cloud top heights were used for the computation of cloud occurrence frequencies. The horizontal and vertical distributions are in good agreement with the SAGE II subvisual cirrus cloud climatology. Seasonal variations, strong longitudinal variability and indications of enhanced cloud occurrence frequencies during the El Nino 9495 and 9798 events have been detected.