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A new cirrus detection algorithm for the Spinning Enhanced Visibleand Infra-Red Imager (SEVIRI) aboard the geostationaryMeteosat Second Generation (MSG), MeCiDA, is presented.The algorithm uses the seven infraredchannels of SEVIRI and thus provides a consistent scheme for cirrusdetection at day and night. MeCiDA combines morphologicaland multi-spectral threshold tests and detects optically thick and thinice clouds. The thresholds were determined by a comprehensive theoreticalstudy using radiative transfer simulations for various atmosphericsituations as well as by manually evaluating actual satelliteobservations. The cirrus detection has been optimized for mid- and highlatitudes but it could be adapted to other regions as well.The retrieved cirrus masks have been validated by comparison with theModerate Resolution Imaging Spectroradiometer (MODIS) Cirrus ReflectionFlag. To study possible seasonal variations in the performance of thealgorithm, one scene per month of the year 2004 was randomly selected andcompared with the MODIS flag. 81% of the pixels wereclassified identically by both algorithms. In a comparison of monthly mean valuesfor Europe and the North-Atlantic MeCiDA detected 29.3% cirrus coverage, whilethe MODIS SWIR cirrus coverage was 38.1%. A lower detection efficiency is to be expected forMeCiDA, as the spatial resolution of MODIS is considerably better andas we used only the thermal infrared channels in contrast to theMODIS algorithm which uses infrared and visible radiances. The advantageof MeCiDA compared to retrievals for polar orbiting instruments orprevious geostationary satellites is that it permits the derivation of quantitativedata every 15 min, 24 h a day. This high temporal resolution allowsthe study of diurnal variations and life cycle aspects. MeCiDA is fast enough fornear real-time applications

Technical note: A new day- and night-time Meteosat Second Generation Cirrus Detection Algorithm MeCiDA