Do Galactic Cosmic Rays Impact the Cirrus Cloud Cover?

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Abstract

Atmospheric ions produced through solar-modulated galactic cosmic rays can promote both the nucleation and the growth of aerosols. The potential impact on the cloud cover is subject of current debates. The CAWSES project SAGACITY (SAtellite and model studies of GAlactic cosmic rays and Clouds modulated by solar activITY) focuses on the statistical analysis of this link, using MIPAS-E satellite data. The extinction data, the cloud occurrence frequency, and the cloud index data from MIPAS-E are correlated with the data from the Climax neutron monitor. A superposed epoch analysis of 6 selected Forbush decrease events yields several weak but statistically significant correlations with an excess of positive cloud-GCR correlations. The impact of a 15 % increase in the Climax neutron monitor data is estimated to result in a small decrease in cloud index (corresponding to an increase in cloud opacity) which is most pronounced at 9 km altitude (−9 % to +0.5 %).

Cornelius Schiller is deceased.