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| Titel |
Decay of the Dst field of geomagnetic disturbance after substorm onset and its implication to storm-substorm relation |
| VerfasserIn |
T. Iyemori, D. R. K. Rao |
| 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 ; 14, no. 6 ; Nr. 14, no. 6, S.608-618 |
| Datensatznummer |
250012320
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| Publikation (Nr.) |
 copernicus.org/angeo-14-608-1996.pdf |
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| Zusammenfassung |
| In order to investigate the causal
relationship between magnetic storms and substorms, variations of the
mid-latitude geomagnetic indices, ASY (asymmetric part) and SYM (symmetric
part), at substorm onsets are examined. Substorm onsets are defined by three
different phenomena; (1) a rapid increase in the mid-latitude
asymmetric-disturbance indices, ASY-D and ASY-H, with a shape of so-called
`mid-latitude positive bay\'; (2) a sharp decrease in the AL index; (3) an onset
of Pi2 geomagnetic pulsation. The positive bays are selected using eye
inspection and a pattern-matching technique. The 1-min-resolution SYM-H index,
which is essentially the same as the hourly Dst index except in terms of the
time resolution, does not show any statistically significant development after
the onset of substorms; it tends to decay after the onset rather than to
develop. It is suggested by a simple model calculation that the decay of the
magnetospheric tail current after substorm onset is responsible for the decay of
the Dst field. The relation between the IMF southward turning and the
development of the Dst field is re-examined. The results support the idea that
the geomagnetic storms and substorms are independent processes; that is, the
ring-current development is not the result of the frequent occurrence of
substorms, but that of enhanced convection caused by the large southward IMF. A
substorm is the process of energy dissipation in the magnetosphere, and its
contribution to the storm-time ring-current formation seems to be negligible.
The decay of the Dst field after a substorm onset is explained by a
magnetospheric energy theorem. |
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