© Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License. Atmospheric Chemistry and Physics Cosmic rays, cloud condensation nuclei and clouds – a reassessment

Abstract. The response of clouds to sudden decreases in the flux of galactic cosmic rays (GCR) – Forbush decrease events – has been investigated using cloud products from the space-borne MODIS instrument, which has been in opera-tion since 2000. By focusing on pristine Southern Hemi-sphere ocean regions we examine areas where we believe that a cosmic ray signal should be easier to detect than else-where. While previous studies have mainly considered cloud cover, the high spatial and spectral resolution of MODIS al-lows for a more thorough study of microphysical parameters such as cloud droplet size, cloud water content and cloud op-tical depth, in addition to cloud cover. Averaging the results from the 22 Forbush decrease events that were considered, no statistically significant correlations were found between any of the four cloud parameters and GCR, when autocorre