The Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) is a five telescope package, which has been developed for the Solar Terrestrial Relation Observatory (STEREO) mission by the Naval Research Laboratory (USA), the Lockheed Solar and Astrophysics Laboratory (USA), the Goddard Space Flight Center (USA), the University of Birmingham (UK), the Rutherford Appleton Laboratory (UK), the Max Planck Institute for Solar System Research (Germany), the Centre Spatiale de Leige (Belgium), the Institut d'Optique (France) and the Institut d'Astrophysique Spatiale (France). SECCHI comprises five telescopes, which together image the solar corona from the solar disk to beyond 1 AU. These telescopes are: an extreme ultraviolet imager (EUVI: 1-1.7 R ), two traditional Lyot coronagraphs (COR1: 1.5-4 R and COR2: 2.5-15 R ) and two new designs of heliospheric imagers (HI-1: 15-84 R and HI-2: 66-318 R ). All the instruments use 2048 × 2048 pixel CCD arrays in a backside-in mode. The EUVI backside surface has been specially processed for EUV sensitivity, while the others have an anti-reflection coating applied. A multi-tasking operating system, running on a PowerPC CPU, receives commands from the spacecraft, controls the instrument operations, acquires the images and compresses them for downlink through the main science channel (at compression factors typically up to 20×) and also through a low bandwidth channel to be used for space weather forecasting (at compression factors up to 200×). An image compression factor of about 10× enable the collection of images at the rate of about one every 2-3 minutes. Identical instruments, except for different sizes of occulters, are included on the STEREO-A and STEREO-B spacecraft.
Abstract. An earth-directed coronal mass ejection (CME) was observed on May 12, 1997 by the SOHO Extreme ultraviolet Imaging Telescope (EIT). The CME, originating north of the central solar meridian, was later observed by the Large Angle Spectrometric Coronagraph (LASCO) as a "halo" CME: a bright expanding ring centered about the occulting disk. Beginning at about 04:35 UT, EIT recorded several CME signatures, including dimming regions close to the eruption, post-eruption arcade formation, and a bright wavefront propagating quasi-radially from the source region. Each of these phenomena appear to be associated with the same eruption, and the onset time of these features corresponds with the estimated onset time observed in LASCO. We discuss the correspondence of these features as observed by EIT with the structure of the CME in the LASCO data.
Mounted on the sides of two widely separated spacecraft, the two Heliospheric Imager (HI) instruments onboard NASA's STEREO mission view, for the first time, the space between the Sun and Earth. These instruments are wide-angle visible-light imagers that incorporate sufficient baffling to eliminate scattered light to the extent that the passage of solar coronal mass ejections (CMEs) through the heliosphere can be detected. Each HI instrument comprises two cameras, HI-1 and HI-2, which have 20°and 70°fields of view and are off-pointed from the Sun direction by 14.0°and 53.7°, respectively, with their optical axes aligned in the ecliptic plane. This arrangement provides coverage over solar elongation angles from 4.0°to 88.7°at the viewpoints of the two spacecraft, thereby allowing the observation of Earth-directed CMEs along the Sun -Earth line to the vicinity of the Earth and beyond. Given the two separated platforms, this also presents the first opportunity to view the structure and evolution of CMEs in three dimensions. The STEREO spacecraft were launched from Cape Canaveral Air Force Base in late October 2006, and the HI instruments have been performing scientific observations since early 2007. The design, development, manufacture, and calibration of these unique instruments are reviewed in this paper. Mission operations, including the initial commissioning phase and the science operations phase, are described. Data processing and analysis procedures are briefly discussed, and groundtest results and in-orbit observations are used to demonstrate that the performance of the instruments meets the original scientific requirements.
During relatively quiet solar conditions throughout the spring and summer of 2007, the SECCHI HI2 white-light telescope on the STEREO B solar-orbiting spacecraft observed a succession of wave fronts sweeping past Earth. We have compared these heliospheric images with in situ plasma and magnetic field measurements obtained by nearEarth spacecraft, and we have found a near perfect association between the occurrence of these waves and the arrival of density enhancements at the leading edges of high-speed solar wind streams. Virtually all of the strong corotating interaction regions are accompanied by large-scale waves, and the low-density regions between them lack such waves. Because the Sun was dominated by long-lived coronal holes and recurrent solar wind streams during this interval, there is little doubt that we have been observing the compression regions that are formed at low latitude as solar rotation causes the high-speed wind from coronal holes to run into lower speed wind ahead of it. Subject headingg s: Sun: corona -Sun: coronal mass ejections (CMEs) -Sun: magnetic fields
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