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| Titel |
STEREO observations of interplanetary coronal mass ejections and prominence deflection during solar minimum period |
| VerfasserIn |
E. K. J. Kilpua, J. Pomoell, A. Vourlidas, R. Vainio, J. Luhmann, Y. Li, P. Schroeder, A. B. Galvin, K. Simunac |
| 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. 12 ; Nr. 27, no. 12 (2009-12-10), S.4491-4503 |
| Datensatznummer |
250016726
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| Publikation (Nr.) |
 copernicus.org/angeo-27-4491-2009.pdf |
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| Zusammenfassung |
In this paper we study the occurrence rate and solar origin of interplanetary
coronal mass ejections (ICMEs) using data from the two Solar TErrestrial
RElation Observatory (STEREO) and the Wind spacecraft. We perform a
statistical survey of ICMEs during the late declining phase of solar cycle
23. Observations by multiple, well-separated spacecraft show that even at the
time of extremely weak solar activity a considerable number of ICMEs were
present in the interplanetary medium. Soon after the beginning of the STEREO
science mission in January 2007 the number of ICMEs declined to less than one
ICME per month, but in late 2008 the ICME rate clearly increased at each
spacecraft although no apparent increase in the number of coronal mass
ejections (CMEs) occurred. We suggest that the near-ecliptic ICME rate can
increase due to CMEs that have been guided towards the equator from their
high-latitude source regions by the magnetic fields in the polar coronal
holes.
We consider two case studies to highlight the effects of the polar magnetic
fields and CME deflection taking advantage of STEREO observations when the
two spacecraft were in the quadrature configuration (i.e. separated by about
90 degrees). We study in detail the solar and interplanetary consequences of
two CMEs that both originated from high-latitude source regions on 2
November 2008. The first CME was slow (radial speed 298 km/s) and associated
with a huge polar crown prominence eruption. The CME was guided by polar
coronal hole fields to the equator and it produced a clear flux rope ICME in
the near-ecliptic solar wind. The second CME (radial speed 438 km/s)
originated from an active region 11007 at latitude 35° N. This CME
propagated clearly north of the first CME and no interplanetary consequences
were identified. The two case studies suggest that slow and elongated CMEs
have difficulties overcoming the straining effect of the overlying field and
as a consequence they are guided by the polar coronal fields and cause
in-situ effects close to the ecliptic plane. The 3-D propagation directions
and CME widths obtained by using the forward modelling technique were
consistent with the solar and in-situ observations. |
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