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| Titel |
Latitude dependence of long-term geomagnetic activity and its solar wind drivers |
| VerfasserIn |
M. Myllys, N. Partamies, L. Juusola |
| 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 ; 33, no. 5 ; Nr. 33, no. 5 (2015-05-28), S.573-581 |
| Datensatznummer |
250121198
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| Publikation (Nr.) |
 copernicus.org/angeo-33-573-2015.pdf |
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| Zusammenfassung |
| To validate the usage of global indices in studies of geomagnetic activity,
we have examined the latitude dependence of geomagnetic variations in
Fennoscandia and Svalbard from 1994 to 2010. Daily standard deviation (SD)
values of the horizontal magnetic field have been used as a measure of the
ground magnetic disturbance level. We found that the timing of the
geomagnetic minimum depends on the latitude region: corresponding to the
minimum of sunspot cycle 22 (in 1996), the geomagnetic minimum occurred between the geomagnetic latitudes 57–61° in 1996 and at
the latitudes 64–67° in 1997, which are the average auroral oval latitudes.
During sunspot cycle 23, all latitude regions experienced the minimum in
2009, a year after the sunspot minimum. These timing differences are due to
the latitude dependence of the 10 s daily SD on the different solar wind
drivers. In the latitude region of 64–67°, the impact of the
high-speed solar wind streams (HSSs) on the geomagnetic activity is the most
pronounced compared to the other latitude groups, while in the latitude
region of 57–61°, the importance of the coronal mass ejections (CMEs)
dominates. The geomagnetic activity maxima during ascending solar cycle
phases are typically caused by CME activity and occur especially in the oval
and sub-auroral regions. The strongest geomagnetic activity occurs during the
descending solar cycle phases due to a mixture of CME and HSS activity.
Closer to the solar minimum, less severe geomagnetic activity is driven by
HSSs and mainly visible in the poleward part of the auroral region. According
to our study, however, the timing of the geomagnetic activity minima (and
maxima) in different latitude bands is different, due to the relative
importance of different solar wind drivers at different latitudes. |
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