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| Titel |
On the role of clouds in the fair weather part of the global electric circuit |
| VerfasserIn |
A. J. G. Baumgaertner, G. M. Lucas, J. P. Thayer, S. A. Mallios |
| 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 ; 14, no. 16 ; Nr. 14, no. 16 (2014-08-25), S.8599-8610 |
| Datensatznummer |
250118973
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| Publikation (Nr.) |
 copernicus.org/acp-14-8599-2014.pdf |
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| Zusammenfassung |
| Clouds in the fair weather return path of the global electric circuit (GEC)
reduce conductivity because of the limited mobility of charge due to
attachment to cloud water droplets, effectively leading to a loss of ions. A
high-resolution GEC model, which numerically solves the current continuity
equation in combination with Ohm's law, is used to show that return currents
partially flow around clouds, with current divergence above the cloud and
convergence below the cloud. An analysis of this effect is presented for
various types of clouds, i.e., for different altitude extents and for
different horizontal dimensions, finding that the effect is most pronounced
for high clouds with a diameter below 100 km. Based on these results, a
method to calculate column and global resistance is developed that can
account for all cloud sizes and altitudes. The
CESM1(WACCM) (Community Earth System Model – Whole Atmosphere Community
Climate Model) as well as ISCCP (International Satellite Cloud
Climatology Project) cloud data are used to calculate the effect of this
phenomenon on global resistance. From CESM1(WACCM), it is found that when
including clouds in the estimate of resistance the global resistance
increases by up to 73%, depending on the parameters used. Using ISCCP
cloud cover leads to an even larger increase, which is likely to be
overestimated because of time averaging of cloud cover. Neglecting current
divergence/convergence around small clouds overestimates global resistance by
up to 20% whereas the method introduced by previous studies
underestimates global resistance by up to 40%. For global GEC models,
a~conductivity parameterization is developed to account for the current
divergence/convergence phenomenon around clouds. Conductivity simulations
from CESM1(WACCM) using this parameterization are presented. |
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