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| Titel |
Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models |
| VerfasserIn |
K. Marubashi, R. P. Lepping |
| 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 ; 25, no. 11 ; Nr. 25, no. 11 (2007-11-29), S.2453-2477 |
| Datensatznummer |
250015953
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| Publikation (Nr.) |
 copernicus.org/angeo-25-2453-2007.pdf |
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| Zusammenfassung |
| We identified 17 magnetic clouds (MCs) with durations
longer than 30 h, surveying the solar wind data obtained by the WIND and
ACE spacecraft during 10 years from 1995 through 2004. Then, the magnetic
field structures of these 17 MCs were analyzed by the technique of the
least-squares fitting to force-free flux rope models. The analysis was made
with both the cylinder and torus models when possible, and the results from
the two models are compared. The torus model was used in order to
approximate the curved portion of the MCs near the flanks of the MC loops.
As a result, we classified the 17 MCs into 4 groups. They are (1) 5 MC
events exhibiting magnetic field rotations through angles substantially
larger than 180° which can be interpreted only by the torus model; (2) 3
other MC events that can be interpreted only by the torus model as well,
though the rotation angles of magnetic fields are less than 180°; (3) 3
MC events for which similar geometries are obtained from both the torus and
cylinder models; and (4) 6 MC events for which the resultant geometries
obtained from both models are substantially different from each other, even
though the observed magnetic field variations can be interpreted by either
of the torus model or the cylinder model. It is concluded that the MC events
in the first and second groups correspond to those cases where the
spacecraft traversed the MCs near the flanks of the MC loops, the difference
between the two being attributed to the difference in distance between the
torus axis and the spacecraft trajectory. The MC events in the third group
are interpreted as the cases where the spacecraft traversed near the apexes
of the MC loops. For the MC events in the fourth group, the real geometry
cannot be determined from the model fitting technique alone. Though an
attempt was made to determine which model is more plausible for each of the
MCs in this group by comparing the characteristics of associated
bidirectional electron heat flows, the results were not very definitive. It
was also found that the radii of the flux ropes obtained from the torus
fitting tend to be generally smaller than those obtained from the cylinder
fitting. This result raises a possible problem in estimating the magnetic
flux and helicity carried away from the Sun by the MCs. |
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