A streamer is a bright (dense) structure containing closed and open fields, which help guide denser, outward-flowing solar wind material. They are observed by coronagraphs (and during solar eclipses) above the solar limb and are often found above active regions. Blowout CMEs viewed when the surface eruption is at the solar limb mostly display the classic three-part structure (Burkepile et al., 2004). In these cases prominence material can actually be followed from at or near the solar surface (as viewed in the H line) into the coronagraph field of view (Figures 2, 19, and 20), where it forms the bright core of the CME. CMEs exhibit radial velocity dispersion, with the leading edge being fastest, followed by the speed decreasing through the prominence material (Webb and Jackson, 1981; Simnett, 2000). The kinematic profiles of erupting prominences and their associated CMEs are usually similar in that both will exhibit acceleration, deceleration or constant speed with height. The SMM coronagraph had an H filter, which was used for studies of a few CMEs containing large prominences. Illing and Athay (1986) compared the H and white light images from eight prominence/CMEs finding that some CME prominence masses exceed 1012 kg: a large fraction of the total CME mass. They also concluded that the prominence material usually becomes nearly fully ionized as it moves outward through the low corona. UVCS results are limited in this regard, because its best diagnostics are for plasma typically in the 105 K range. The brightest UVCS emission seen during CMEs is likely in the core or prominence material. Proton temperatures and ionization states suggest plasma of 104.5 – 5.5 K, so the material has probably been heated from the original prominence temperatures and it must be heated continually as it moves out to counteract cooling and radiative losses (Kohl et al., 2006; J. Raymond, 2011, priv. comm.). In one event, Ciaravella et al. (2003b) noted that prominence material likely was heated to above 106 K. The cleanest evidence for heated prominence plasma is the EIS result for the 9 April 2008 event by Landi et al. (2010). Also, many EIT and TRACE observations of erupting prominences near the surface show them changing from absorption to emission, indicative of heating.
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Living Rev. Solar Phys. 9, (2012), 3
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