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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D6, 4195, doi:10.1029/2001JD001264, 2003

Galactic cosmic ray and El Niño–Southern Oscillation trends in International Satellite Cloud Climatology Project D2 low-cloud properties

Nigel Marsh

Danish Space Research Institute, Copenhagen, Denmark


Henrik Svensmark

Danish Space Research Institute, Copenhagen, Denmark


Abstract

The recently reported correlation between clouds and galactic cosmic rays (GCR) implies the existence of a previously unknown process linking solar variability and climate. An analysis of the interannual variability of International Satellite Cloud Climatology Project D2 (ISCCP-D2) low-cloud properties over the period July 1983 to August 1994 suggests that low clouds are statistically related to two processes, (1) GCR and (2) El Niño–Southern Oscillation (ENSO), with GCR explaining a greater percentage of the total variance. Areas where satellites have an unobstructed view of low cloud possess a strong correlation with GCR, which suggests that low-cloud properties observed in these regions are less likely to be contaminated from overlying cloud. The GCR-low cloud correlation cannot easily be explained by internal climate processes, changes in direct solar forcing, or UV-ozone interactions. Instead, it is argued that a mechanism involving solar variability via GCR ionization of the atmosphere is consistent with these results. However, the results are marginal when including the recently extended ISCCP-D2 data covering the period until September 2001. This, we believe, is related to problems experienced with the ISCCP intercalibration between September 1994 and January 1995.

Published 29 March 2003.

Index Terms: 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 1650 Global Change: Solar variability; 1620 Global Change: Climate dynamics (3309); 2104 Interplanetary Physics: Cosmic rays.

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Citation: Marsh, N., and H. Svensmark (2003), Galactic cosmic ray and El Niño–Southern Oscillation trends in International Satellite Cloud Climatology Project D2 low-cloud properties, J. Geophys. Res., 108(D6), 4195, doi:10.1029/2001JD001264.