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). 01/2005; 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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    • "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.
    Annales Geophysicae 07/2013; 31:1251-1265. DOI:10.5194/angeo-31-1251-2013 · 1.71 Impact Factor
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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.
    Annales Geophysicae 11/2009; 27(11). DOI:10.5194/angeo-27-4349-2009 · 1.71 Impact Factor
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    ABSTRACT: The solar wind is a highly supersonic outflow of coronal plasma flowing in a close to radial direction out from the Sun. Generally, there are two modes of outflow, a fast stream mode with velocities in the range of 750 kms−1 to 800 kms−1, and a slow stream mode with velocities in the range of 350 kms−1 to 400 kms−1. The method of interplanetary scintillation (IPS) is used to obtain solar wind velocity estimates by observing the “twinkling” of radio waves from distant compact sources caused by density variations in the solar wind. The Aberystwyth IPS group has been conducting IPS observations using the European Incoherent SCATter radar (EISCAT) in northern Scandinavia since 1993 and more recently using the Multi-Element Radio-Linked Interferometer Network (MERLIN) radio telescopes in the United Kingdom. This thesis investigates the large-scale structure of the solar wind using IPS observations in conjunction with white-light, extreme ultra-violet (EUV) and X-ray Carrington rotation maps from ground-based: Mauna Loa; and space-based: SOlar and Heliospheric Observatory (SOHO) and Yohkoh; as well as in-situ spacecraft observations of solar wind velocity from Wind and Ulysses. A complete study of EISCAT IPS data from 1994 to 2003 is undertaken looking for detections of interaction in terms of shear layers and co-rotating interaction regions (CIRs) by ballistically mapping the IPS observations out to in-situ distances to see how interaction develops. From this, an investigation was carried out with solar minimum (1994-1997) EISCAT IPS data investigating a possible bi-modal fast solar wind structure. In addition, the technique of extremely long-baseline IPS measurements (developed from 2002) was used to look at the finer structure of solar wind velocity. This technique was also used to investigate the direction of flow which included observations of fast and slow wind, interaction regions, and the passage of a magnetic cloud. PPARC
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