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| Titel |
The spatial relationship between active regions and coronal holes and the occurrence of intense geomagnetic storms throughout the solar activity cycle |
| VerfasserIn |
S. Bravo, J. A. L. Cruz-Abeyro, D. Rojas |
| 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 ; 16, no. 1 ; Nr. 16, no. 1, S.49-54 |
| Datensatznummer |
250013101
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| Publikation (Nr.) |
 copernicus.org/angeo-16-49-1998.pdf |
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| Zusammenfassung |
| We study the annual frequency of occurrence
of intense geomagnetic storms (Dst < –100 nT) throughout the solar
activity cycle for the last three cycles and find that it shows different
structures. In cycles 20 and 22 it peaks during the ascending phase, near
sunspot maximum. During cycle 21, however, there is one peak in the ascending
phase and a second, higher, peak in the descending phase separated by a minimum
of storm occurrence during 1980, the sunspot maximum. We compare the solar cycle
distribution of storms with the corresponding evolution of coronal mass
ejections and flares. We find that, as the frequency of occurrence of coronal
mass ejections seems to follow very closely the evolution of the sunspot number,
it does not reproduce the storm profiles. The temporal distribution of flares
varies from that of sunspots and is more in agreement with the distribution of
intense geomagnetic storms, but flares show a maximum at every sunspot maximum
and cannot then explain the small number of intense storms in 1980. In a
previous study we demonstrated that, in most cases, the occurrence of intense
geomagnetic storms is associated with a flaring event in an active region
located near a coronal hole. In this work we study the spatial relationship
between active regions and coronal holes for solar cycles 21 and 22 and find
that it also shows different temporal evolution in each cycle in accordance with
the occurrence of strong geomagnetic storms; although there were many active
regions during 1980, most of the time they were far from coronal holes. We
analyse in detail the situation for the intense geomagnetic storms in 1980 and
show that, in every case, they were associated with a flare in one of the few
active regions adjacent to a coronal hole. |
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