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| Titel |
Statistical analysis of the dependence of large-scale Birkeland currents on solar wind parameters |
| VerfasserIn |
H. Korth, B. J. Anderson, C. L. Waters |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 28, no. 2 ; Nr. 28, no. 2 (2010-02-10), S.515-530 |
| Datensatznummer |
250016781
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| Publikation (Nr.) |
 copernicus.org/angeo-28-515-2010.pdf |
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| Zusammenfassung |
| The spatial distributions of large-scale field-aligned Birkeland currents
have been derived using magnetic field data obtained from the Iridium
constellation of satellites from February 1999 to December 2007. From this
database, we selected intervals that had at least 45% overlap in the
large-scale currents between successive hours. The consistency in the current
distributions is taken to indicate stability of the large-scale
magnetosphere–ionosphere system to within the spatial and temporal resolution
of the Iridium observations. The resulting data set of about 1500 two-hour
intervals (4% of the data) was sorted first by the interplanetary magnetic
field (IMF) GSM clock angle (arctan(By/Bz)) since this
governs the spatial morphology of the currents. The Birkeland current
densities were then corrected for variations in EUV-produced ionospheric
conductance by normalizing the current densities to those occurring for
0° dipole tilt. To determine the dependence of the currents on
other solar wind variables for a given IMF clock angle, the data were then
sorted sequentially by the following parameters: the solar wind electric
field in the plane normal to the Earth–Sun line, Eyz; the solar
wind ram pressure; and the solar wind Alfvén Mach number. The solar wind
electric field is the dominant factor determining the Birkeland current
intensities. The currents shift toward noon and expand equatorward with
increasing solar wind electric field. The total current increases by 0.8 MA
per mV m−1 increase in Eyz for southward IMF, while for northward
IMF it is nearly independent of the electric field, increasing by only 0.1 MA
per mV m−1 increase in Eyz. The dependence on solar wind pressure
is comparatively modest. After correcting for the solar dynamo dependencies
in intensity and distribution, the total current intensity increases with
solar wind dynamic pressure by 0.4 MA/nPa for southward IMF. Normalizing the
Birkeland current densities to both the median solar wind electric field and
dynamic pressure effects, we find no significant dependence of the Birkeland
currents on solar wind Alfvén Mach number. |
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