The radial width of a Coronal Mass Ejection between 0.1 and 0.4 AU estimated from the Heliospheric Imager on STEREO
On 15–17 February 2008, a CME with an approximately circular cross section was tracked through successive images obtained by the Heliospheric Imager (HI) instrument onboard the STEREO-A spacecraft. Reasoning that an idealised flux rope is cylindrical in shape with a circular cross-section, best...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2009-11-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/27/4349/2009/angeo-27-4349-2009.pdf |
| Summary: | On 15–17 February 2008, a CME with an approximately circular cross
section was tracked through successive images obtained by the Heliospheric
Imager (HI) instrument onboard the STEREO-A spacecraft. Reasoning that an
idealised flux rope is cylindrical in shape with a circular cross-section,
best fit circles are used to determine the radial width of the CME. As part
of the process the radial velocity and longitude of propagation are
determined by fits to elongation-time maps as 252±5 km/s and 70±5°
respectively. With the longitude known, the radial size is calculated
from the images, taking projection effects into account. The radial width of
the CME, S (AU), obeys a power law with heliocentric distance, <I>R</I>, as the CME
travels between 0.1 and 0.4 AU, such that S=0.26 <I>R</I><sup>0.6±0.1</sup>. The
exponent value obtained is compared to published studies based on
statistical surveys of in situ spacecraft observations of ICMEs between 0.3
and 1.0 AU, and general agreement is found. This paper demonstrates the new
opportunities provided by HI to track the radial width of CMEs through the
previously unobservable zone between the LASCO field of view and Helios in
situ measurements. |
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| ISSN: | 0992-7689 1432-0576 |