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| Titel |
A superposed epoch analysis of geomagnetic storms |
| VerfasserIn |
J. R. Taylor, Mark Lester, T. K. Yeoman |
| 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 ; 12, no. 7 ; Nr. 12, no. 7, S.612-624 |
| Datensatznummer |
250010970
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| Publikation (Nr.) |
 copernicus.org/angeo-12-612-1994.pdf |
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| Zusammenfassung |
| A superposed epoch analysis of geomagnetic
storms has been undertaken. The storms are categorised via their intensity (as
defined by the Dst index). Storms have also been classified here as
either storm sudden commencements (SSCs) or storm gradual commencements (SGCs,
that is all storms which did not begin with a sudden commencement). The
prevailing solar wind conditions defined by the parameters solar wind speed (vsw),
density (ρsw) and pressure (Psw)
and the total field and the components of the interplanetary magnetic field (IMF)
during the storms in each category have been investigated by a superposed epoch
analysis. The southward component of the IMF, appears to be the controlling
parameter for the generation of small SGCs (-100 nT< minimum Dst ≤ -50
nT for ≥ 4 h), but for SSCs of the same intensity solar wind pressure is
dominant. However, for large SSCs (minimum Dst ≤ -100 nT for ≥ 4 h)
the solar wind speed is the controlling parameter. It is also demonstrated that
for larger storms magnetic activity is not solely driven by the accumulation of
substorm activity, but substantial energy is directly input via the dayside.
Furthermore, there is evidence that SSCs are caused by the passage of a coronal
mass ejection, whereas SGCs result from the passage of a high speed/ slow speed
coronal stream interface. Storms are also grouped by the sign of Bz
during the first hour epoch after the onset. The sign of Bz at
t = +1 h is the dominant sign of the Bz for ~24 h before
the onset. The total energy released during storms for which Bz
was initially positive is, however, of the same order as for storms where Bz
was initially negative. |
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