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| Titel |
Model of optical response of marine aerosols to Forbush decreases |
| VerfasserIn |
T. Bondo, M. B. Enghoff, H. Svensmark |
| 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 ; 10, no. 6 ; Nr. 10, no. 6 (2010-03-24), S.2765-2776 |
| Datensatznummer |
250008255
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| Publikation (Nr.) |
 copernicus.org/acp-10-2765-2010.pdf |
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| Zusammenfassung |
| In order to elucidate the effect of galactic cosmic rays on cloud formation,
we investigate the optical response of marine aerosols to Forbush decreases
– abrupt decreases in galactic cosmic rays – by means of modeling. We vary
the nucleation rate of new aerosols, in a sectional coagulation and
condensation model, according to changes in ionization by the Forbush
decrease. From the resulting size distribution we then calculate the aerosol
optical thickness and Angstrom exponent, for the wavelength pairs 350,
450 nm and 550, 900 nm. In the cases where the output parameters from the
model seem to compare best with atmospheric observations we observe, for the
shorter wavelength pair, a change in Angstrom exponent, following the Forbush
Decrease, of −6 to +3%. In some cases we also observe a delay in the
change of Angstrom exponent, compared to the maximum of the Forbush decrease,
which is caused by different sensitivities of the probing wavelengths to
changes in aerosol number concentration and size. For the long wavelengths
these changes are generally smaller. The types and magnitude of change is
investigated for a suite of nucleation rates, condensable gas production
rates, and aerosol loss rates. Furthermore we compare the model output with
observations of 5 of the largest Forbush decreases after year 2000. For the
350, 450 nm pair we use AERONET data and find a comparable change in signal
while the Angstrom Exponent is lower in the model than in the data, due to
AERONET being mainly sampled over land. For 550, 900 nm we compare with both
AERONET and MODIS and find little to no response in both model and
observations. In summary our study shows that the optical properties of
aerosols show a distinct response to Forbush Decreases, assuming that the
nucleation of fresh aerosols is driven by ions. Shorter wavelengths seem more
favorable for observing these effects and great care should be taken when
analyzing observations, in order to avoid the signal being drowned out by
noise. |
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