Mass estimates of a few CMEs have also been made with radio (Gopalswamy and Kundu, 1993; Ramesh et al., 2003) and X-ray observations (e.g., Rust and Hildner, 1976; Hudson and Webb, 1997) and, more recently, in the EUV (e.g., Harrison et al., 2003; Aschwanden et al., 2009). Many X-ray and EUV measurements involve “coronal dimming” (Section 3.4) regions associated with a CME, and these estimates are usually lower than that of the equivalent white light masses. This is probably because the material leaving the coronal dimming region is only part of that comprised in the CME. The radio, X-ray, and EUV techniques provide an independent check on CME masses because their dependency is on the thermal properties of the plasma (density and temperature) vs only density in the white light observations. Likewise average CME kinetic energies measured by LASCO are less than previous measurements, 2.0 × 1030 erg (Vourlidas et al., 2010 – Figure 16). The CME kinetic energy distribution appears to have a power law index of –1 (Vourlidas et al., 2002a), different than that for flares (–2; Hudson, 1991; Yashiro et al., 2006).
Figure 18 shows plots of the solar-cycle dependence of the LASCO CME mass and kinetic energy (Vourlidas et al., 2010, 2011b). The bottom panel shows the total CME mass per Carrington rotation. The mass, mass density, and kinetic energy all have minima in 2007 that are 2 – 4 times below the 1996 minimum and reflect the unusual extended activity in Solar Cycle 23. The total mass reaches a minimum in 2009 and is roughly equivalent to the 1996 minimum. MacQueen et al. (2001) found that the mass density variation between Solar Cycle 22 minimum and maximum varied by a factor 4 even in the background corona.
Measuring CME masses and energies using white light images farther from the Sun has proven to be a difficult task (see Section 5.3), due to the lack of calibration information and the uncertainties imposed by the faintness of the CMEs compared to the background noise. Mass and energy estimates have also been made from 3-D density reconstructions of a few CMEs observed in the heliosphere by SMEI (Jackson et al., 2008a, 2010a). The mass estimates generally agree with the mass of the same CMEs as derived from LASCO data. Some attempts are currently being made using some highly developed processing techniques with the STEREO SECCHI images. DeForest et al. (2012) performed some mass measurements on a small disconnection event (i.e., not a CME) using photometric measurements and the theory of Thomson scattering. The technique is currently being applied to CME measurements.
The reader must note that as with the kinematical properties, mass calculations are based on coronagraph images and, therefore, subject to the same problems of projection and perspective. For example, the CME mass calculations in the CDAW catalog make the assumption that all of the CME mass is in the sky plane, as has always been the standard assumption. The Thomson scattering theory from which the density is derived includes a direction term , and so the direction of propagation is an integral component of the density calculations. Traditionally, auxiliary data such as solar flare or filament location have been used provide an estimate of CME direction but more recent work making use of the stereoscopic capabilities of STEREO have provided more accurate measurements (Colaninno and Vourlidas, 2009). Finally, the Thomson scattering theory provided by Billings differs somewhat from the initial treatment by Schuster (1879) and Minneart (1930). An alternative treatment of this theory and it applications to both coronagraphs and heliospheric imagers can be found in Howard and Tappin (2009), Howard (2011a) and Howard and DeForest (2012b). This latest theory implies that the sky plane assumption may be more appropriate than has been previously assumed (see also van Houten, 1950).
A poorly understood topic is that of the energy budget available to the eruption of CMEs and associated solar activity. The next section discusses many of the phenomena that are known to be associated with CMEs and all of them require substantial quantities of energy. If we assume that the total energy arises from magnetic energy stored in the pre-launch corona then we may allocate an energy budget for the CME and its associated phenomena. Few studies have been conducted to address this topic, largely because of the difficulty in acquiring accurate measurements of both the available budget and the energies available from each associated phenomenon. These publications have revealed that the mechanical energy consumed by the launch and evolution of a CME is much greater than that of all the associated eruptive phenomena combined. Canfield et al. (1980), Webb et al. (1980), and Emslie et al. (2004) found the CME mechanical energy to be an order of magnitude greater than that of the associated flare and to consume the majority of energy available from the magnetic field. Ravindra and Howard (2010) found the mechanical energy of the CME was over an order of magnitude greater than that of the associated flare, and that half-to-all of the energy removed from the magnetic field during the eruption was consumed by the flare-CME-associated eruption combination. The uncertainties associated with the calculations in all of these studies, unfortunately, are too large to draw any firm conclusions.
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