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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
01 Feb 2012
Review status
This discussion paper is a preprint. It has been under review for the journal Atmospheric Chemistry and Physics (ACP). The revised manuscript was not accepted.
Effects of cosmic ray decreases on cloud microphysics
J. Svensmark, M. B. Enghoff, and H. Svensmark National Space Institute, Technical University of Denmark, Copenhagen, Denmark
Abstract. Using cloud data from MODIS we investigate the response of cloud microphysics to sudden decreases in galactic cosmic radiation – Forbush decreases – and find responses in effective emissivity, cloud fraction, liquid water content, and optical thickness above the 2–3 sigma level 6–9 days after the minimum in atmospheric ionization and less significant responses for effective radius and cloud condensation nuclei (<2 sigma). The magnitude of the signals agree with derived values, based on simple equations for atmospheric parameters. Furthermore principal components analysis gives a total significance of the signal of 3.1 sigma. We also see a correlation between total solar irradiance and strong Forbush decreases but a clear mechanism connecting this to cloud properties is lacking. There is no signal in the UV radiation. The responses of the parameters correlate linearly with the reduction in the cosmic ray ionization. These results support the suggestion that ions play a significant role in the life-cycle of clouds.
Citation: Svensmark, J., Enghoff, M. B., and Svensmark, H.: Effects of cosmic ray decreases on cloud microphysics, Atmos. Chem. Phys. Discuss., 12, 3595-3617,, 2012.
J. Svensmark et al.


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