The STEREO heliospheric imager: how to detect CMEs in the heliosphere

School of Physics and Astronomy, University of Birmingham, Birmingham, England, United Kingdom
Advances in Space Research (Impact Factor: 1.36). 12/2005; 36(8):1512-1523. DOI: 10.1016/j.asr.2005.01.024


The STEREO Heliospheric Imager is a wide-angle imaging system that will enable, for the first time, a view of Earth-directed coronal mass ejections (CMEs) in a field of view which also encompasses the Earth. Twin views from widely spaced platforms, combined with the out of Sun–Earth line perspective allow a unique and powerful tool for the study of CMEs and, particularly, Earth-directed CMEs. We outline the instrumental characteristics and image simulation studies which reveal the nature of the images we anticipate.

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Available from: C. J. Eyles, Oct 04, 2015
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    • "The connection between white-light and in situ disturbances was established soon after the discovery of CMEs (e.g., Sheeley et al., 1983). Although CMEs can be now followed with heliospheric imagers (SMEI/Coriolis, Eyles et al., 2003; SECCHI/STEREO Harrison et al., 2005) to the orbit of the Earth (e.g., Tappin et al., 2004; Harrison et al., 2009), linking remote CME observations to the structure of their in situ counterparts is not straightforward. The whitelight morphology is difficult to interpret as the images represent a line-of-sight projection of optically thin structures and because CME emission becomes increasingly fainter the further out in the heliosphere the CME travels (e.g., Lugaz et al., 2005; Howard and Tappin, 2009; Rouillard, 2011). "
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    ABSTRACT: The relationship of magnetic clouds (MCs) to interplanetary coronal mass ejections (ICMEs) is still an open issue in space research. The view that all ICMEs would originate as magnetic flux ropes has received increasing attention, although near the orbit of the Earth only about one-third of ICMEs show clear MC signatures and often the MC occupies only a portion of the ICME. We have performed a systematic comparison of the cases where ICME and MC signatures coincided and where ICME signatures extended significantly beyond the MC boundaries. We found clear differences in the ICME properties (eg., speed, magnetic field magnitude), in the ambient solar wind structure, and in the solar cycle dependence for these two event types. We show that the MC and the regions of ICME-related plasma in front and behind the MC have all distinct characteristics enforcing the conception that they have intrinsically different origin or evolve differently. Erosion of magnetic flux in front of the ICME may also reconfigure the initial three-part CME seen in white-light images to a more complex ICME, but the geometrical effect (i.e. the encounter through the CME leg and/or far from the flux rope center) has little contribution to the observed mismathch in the MC and ICME boundary times. We will also discuss ramifications to CME and space weather research.
    Full-text · Article · Jul 2013 · Annales Geophysicae
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    • "At the time of the events studied here, the two STEREO spacecraft provided near‐quadrature observations of the solar corona with the SECCHI EUV and coronagraph imagers [Howard et al., 2008] and of the inner heliosphere with the SECCHI Heliospheric Imagers [Harrison et al., 2005]. On 1 August 2010, STEREO Behind was trailing the Sun‐Earth line (then over Carrington longitude 107.3°) by 70.8° (thus putting it over Carrington longitude 36.5°), and STEREO Ahead was leading it by 78.9° (over Carrington longitude 186.2°), leaving a wedge of only 30° of the solar surface unobserved. "
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    ABSTRACT: The combination of SDO and STEREO observations enables us to view much of the solar surface and atmosphere simultaneously and continuously. These near-global observations often show near-synchronous long-distance interactions between magnetic domains that exhibit flares, eruptions, and frequent minor forms of activity. Here we analyze a series of flares, filament eruptions, coronal mass ejections, and related events which occurred on 1-2 August 2010. These events extend over a full hemisphere of the Sun, only two-thirds of which is visible from the Earth's perspective. The combination of coronal observations and global field modeling reveals the many connections between these events by magnetic field lines, particularly those at topological divides. We find that all events of substantial coronal activity, including those where flares and eruptions initiate, are connected by a system of separatrices, separators, and quasi-separatrix layers, with little activity within the deep interiors of domains of connectivity. We conclude that for this sequence of events the evolution of field on the hemisphere invisible from Earth's perspective is essential to the evolution, and possibly even to the initiation, of the flares and eruptions over an area that spans at least 180 degrees in longitude. Our findings emphasize that the search for the factors that play a role in the initiation and evolution of eruptive and explosive phenomena, sought after for improved space weather forecasting, requires knowledge of much, if not all, of the solar surface field.
    Preview · Article · Apr 2011 · Journal of Geophysical Research Atmospheres
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    • "This package includes an Extreme Ultraviolet Imager (EUVI), two coronagraphs (COR1 and COR2) and the Heliospheric Imagers (HI) (Eyles et al., 2009). The HI instrument observes in visible light and contains two wide angle cameras on each STEREO spacecraft, HI-1 and HI-2; both are set to view the heliosphere from the edge of the corona with a band-pass of 630–730 nm and 400–1000 nm respectively (Harrison et al., 2005; Eyles et al., 2009). The fields of view centred at 13.7 • and 53.4 • elongation from the Sun and have an angular extent of 20 • and 70 • , respectively (elongation is the angle between the line-of-sight and the line to the Suncentre ). "
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    ABSTRACT: 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, R, as the CME travels between 0.1 and 0.4 AU, such that S=0.26 R0.6±0.1. 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.
    Full-text · Article · Nov 2009 · Annales Geophysicae
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