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| Titel |
Deriving the radial distances of wide coronal mass ejections from elongation measurements in the heliosphere – application to CME-CME interaction |
| VerfasserIn |
N. Lugaz, A. Vourlidas, I. I. Roussev |
| 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 ; 27, no. 9 ; Nr. 27, no. 9 (2009-09-22), S.3479-3488 |
| Datensatznummer |
250016643
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| Publikation (Nr.) |
 copernicus.org/angeo-27-3479-2009.pdf |
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| Zusammenfassung |
| We present general considerations regarding the derivation of the radial
distances of coronal mass ejections (CMEs) from elongation angle measurements
such as those provided by SECCHI and SMEI, focusing on measurements in the
Heliospheric Imager 2 (HI-2) field of view (i.e. past 0.3 AU). This study is
based on a three-dimensional (3-D) magneto-hydrodynamics (MHD) simulation of
two CMEs observed by SECCHI on 24–27 January 2007. Having a 3-D simulation
with synthetic HI images, we are able to compare the two basic methods used
to derive CME positions from elongation angles, the so-called "Point-P" and
"Fixed-φ" approximations. We confirm, following similar works, that
both methods, while valid in the most inner heliosphere, yield increasingly
large errors in HI-2 field of view for fast and wide CMEs. Using a simple
model of a CME as an expanding self-similar sphere, we derive an analytical
relationship between elongation angles and radial distances for wide CMEs.
This relationship is simply the harmonic mean of the "Point-P" and
"Fixed-φ" approximations and it is aimed at complementing 3-D fitting
of CMEs by cone models or flux rope shapes. It proves better at getting the
kinematics of the simulated CME right when we compare the results of our
line-of-sights to the MHD simulation. Based on this approximation, we
re-analyze the J-maps (time-elongation maps) in 26–27 January 2007 and
present the first observational evidence that the merging of CMEs is
associated with a momentum exchange from the faster ejection to the slower
one due to the propagation of the shock wave associated with the fast
eruption through the slow eruption. |
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