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| Titel |
The relationship between the magnetosphere and magnetospheric/auroral substorms |
| VerfasserIn |
S.-I. Akasofu |
| 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 ; 31, no. 3 ; Nr. 31, no. 3 (2013-03-04), S.387-394 |
| Datensatznummer |
250019000
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| Publikation (Nr.) |
 copernicus.org/angeo-31-387-2013.pdf |
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| Zusammenfassung |
On the basis of auroral and polar magnetic substorm studies, the
relationship between the solar wind-magnetosphere dynamo (the DD dynamo)
current and the substorm dynamo (the UL dynamo) current is studied. The
characteristics of both the DD and UL currents reveal why auroral substorms
consist of the three distinct phases after the input power ε is
increased above 1018 erg s−1. (a) The growth phase; the magnetosphere can accumulate
magnetic energy for auroral substorms, when the ionosphere cannot dissipate
the power before the expansion phase. (b) The expansion phase; the magnetosphere releases the
accumulated magnetic energy during the growth phase in a pulse-like manner
in a few hours, because it tries to stabilize itself when the accumulated
energy reaches to about 1023 erg s−1. (c) The recovery phase; the magnetosphere becomes an
ordinary dissipative system after the expansion phase, because the
ionosphere becomes capable of dissipating the power with the rate of
1018 ~ 1019 erg s−1.
On the basis of the above conclusion, it is suggested that the magnetosphere
accomplishes the pulse-like release process (resulting in spectacular
auroral activities) by producing plasma instabilities in the current sheet,
thus reducing the current. The resulting contraction of the magnetic field
lines (expending the accumulated magnetic energy), together with break down
of the "frozen-in" field condition at distances of less than 10 RE,
establishes the substorm dynamo that generates an earthward electric field (Lui and Kamide,
2003; Akasofu, 2011). It is this electric field which manifests as the
expansion phase. A recent satellite observation at a distance of as close as
8.1 RE by Lui (2011) seems to support strongly the occurrence of the chain
of processes suggested in the above.
It is hoped that although the concept presented here is very crude, it will
serve in providing one way of studying the three phases of auroral
substorms. In turn, a better understanding of auroral substorms will also be
useful in studying the magnetosphere, because various auroral activities can
be the visible guide for this endeavor. |
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