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| Titel |
Cosmic rays, cloud condensation nuclei and clouds – a reassessment using MODIS data |
| VerfasserIn |
J. E. Kristjánsson, C. W. Stjern, F. Stordal, A. M. Fjǽraa, G. Myhre, K. Jónasson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 24 ; Nr. 8, no. 24 (2008-12-11), S.7373-7387 |
| Datensatznummer |
250006504
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| Publikation (Nr.) |
 copernicus.org/acp-8-7373-2008.pdf |
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| Zusammenfassung |
| 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 operation
since 2000. By focusing on pristine Southern Hemisphere ocean regions we
examine areas where we believe that a cosmic ray signal should be easier to
detect than elsewhere. While previous studies have mainly considered cloud
cover, the high spatial and spectral resolution of MODIS allows for a more
thorough study of microphysical parameters such as cloud droplet size, cloud
water content and cloud optical 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 autocorrelations were taken into account.
Splitting the area of study into six domains, all of them have a negative
correlation between GCR and cloud droplet size, in agreement with a cosmic
ray – cloud coupling, but in only one of the domains (eastern Atlantic
Ocean) was the correlation statistically significant. Conversely, cloud
optical depth is mostly negatively correlated with GCR, and in the eastern
Atlantic Ocean domain that correlation is statistically significant. For
cloud cover and liquid water path, the correlations with GCR are weaker,
with large variations between the different domains. When only the six
Forbush decrease events with the largest amplitude (more than 10%
decrease) were studied, the correlations fit the hypothesis slightly better,
with 16 out of 24 correlations having the expected sign, although many of
the correlations are quite weak. Introducing a time lag of a few days for
clouds to respond to the cosmic ray signal the correlations tend to become
weaker and even to change sign. |
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