First Imaging of Coronal Mass Ejections in the Heliosphere Viewed from Outside the Sun?–?Earth Line |
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| Authors: | Richard A Harrison Christopher J Davis Christopher J Eyles Danielle Bewsher Steve R Crothers Jackie A Davies Russell A Howard Daniel J Moses Dennis G Socker Jeffrey S Newmark Jean-Philippe Halain Jean-Marc Defise Emmanuel Mazy Pierre Rochus David F Webb George M Simnett |
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| Institution: | (1) Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK;(2) School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK;(3) Grupo de Astronomia y Ciencias del Espacio, ICMUV, Universidad de Valencia, Valencia, Spain;(4) Space Science Division, Naval Research Laboratory, Washington, DC, USA;(5) Centre Spatial de Liège, Université de Liège, ave Pré Aily, 4031 Angleur, Belgium;(6) Institute for Scientific Research, Boston College, Chestnut Hill, MA, USA;(7) Air Force Research Laboratory, Hanscom, AFB, MA, USA |
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| Abstract: | We show for the first time images of solar coronal mass ejections (CMEs) viewed using the Heliospheric Imager (HI) instrument
aboard the NASA STEREO spacecraft. The HI instruments are wide-angle imaging systems designed to detect CMEs in the heliosphere,
in particular, for the first time, observing the propagation of such events along the Sun – Earth line, that is, those directed
towards Earth. At the time of writing the STEREO spacecraft are still close to the Earth and the full advantage of the HI
dual-imaging has yet to be realised. However, even these early results show that despite severe technical challenges in their
design and implementation, the HI instruments can successfully detect CMEs in the heliosphere, and this is an extremely important
milestone for CME research. For the principal event being analysed here we demonstrate an ability to track a CME from the
corona to over 40 degrees. The time – altitude history shows a constant speed of ascent over at least the first 50 solar radii
and some evidence for deceleration at distances of over 20 degrees. Comparisons of associated coronagraph data and the HI
images show that the basic structure of the CME remains clearly intact as it propagates from the corona into the heliosphere.
Extracting the CME signal requires a consideration of the F-coronal intensity distribution, which can be identified from the
HI data. Thus we present the preliminary results on this measured F-coronal intensity and compare these to the modelled F-corona
of Koutchmy and Lamy (IAU Colloq.
85, 63, 1985). This analysis demonstrates that CME material some two orders of magnitude weaker than the F-corona can be detected; a specific
example at 40 solar radii revealed CME intensities as low as 1.7×10−14 of the solar brightness. These observations herald a new era in CME research as we extend our capability for tracking, in
particular, Earth-directed CMEs into the heliosphere. |
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| Keywords: | Coronal mass ejection Heliosphere |
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