The three-part structure is considered to be the standard morphology for CMEs, although observations indicate that only 30% of CME events possess all the three parts (Webb and Hundhausen, 1987). Among the events without a bright core, some are due to that the filament materials drained down to the solar surface along the stretched magnetic field, some are due to that thermal instability had not started to form a filament in the pre-eruption structure, and others might not be related to filament or filament-supporting structure at all.
Based on the Thomson-scattering formulae (see Billings, 1966), the mass of a CME can be estimated (Hundhausen, 1993). Without the knowledge of the exact position of the density-enhanced structure, it is often assumed that the CME is close to the plane of the sky, which would underestimate the mass of the CME, especially for halo events.
Typically, the mass of a CME falls in the range of 1 × 1011 – 4 × 1013 kg, averaged at 3 × 1012 kg (Jackson, 1985; Gopalswamy and Kundu, 1992; Hudson et al., 1996). About 15% of the CMEs have a mass less than 1011 kg (Vourlidas et al., 2002).
Living Rev. Solar Phys. 8, (2011), 1
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