Cosmic ray decreases and changes in the liquid water cloud fraction over the oceans

Abstract

[1] Svensmark et al. (2009) have recently claimed that strong galactic cosmic ray (GCR) decreases during 'Forbush Decrease (FD) events' are followed by decreases in both the global liquid water cloud fraction (LCF) and other closely correlated atmospheric parameters. To test the validity of these findings we have concentrated on just one property, the MODIS LCF and examined two aspects: 1) The statistical chance that the decrease observed in the LCF is abnormal. 2) The likelihood of the observed delay (∼5 to 9 days) being physically connected to the FD events. On both counts we conclude that LCF variations are unrelated to FD events: Both the pattern and timing of observed LCF changes are irreconcilable with current theoretical pathways. Additionally, a zonal analysis of LCF variations also offers no support to the claimed relationship, as the observed anomaly is not found to vary latitudinally in conjunction with cosmic ray intensity. Copyright 2009 by the American Geophysical Union.