The height evolution of the `true CME mass derived from STEREO COR1 and COR2 observations

Using combined STEREO-A and STEREO-B EUVI, COR1 and COR2 data, we derive deprojected CME kinematics and CME `true mass evolutions for a sample of 25 events that occurred during December 2007 to April 2011. We develop a fitting function to describe the CME mass evolution with height. The function considers both the effect of the coronagraph occulter, at the beginning of the CME evolution, and an actual mass increase. The latter becomes important at about 10Rs to 15Rs and is assumed to mostly contribute up to 20Rs. The mass increase ranges from 2% to 6% per Rs and, is positively correlated to the total CME mass. Due to the combination of COR1 and COR2 mass measurements, we are able to estimate the `true mass value for very low coronal heights (< 3Rs). Based on the deprojected CME kinematics and initial ejected masses, we derive the kinetic energies and propelling forces acting on the CME in the low corona (< 3Rs). The derived CME kinetic energies range between 1-66*10^23 J, and the forces range between 2.2-510*10^14 N.

CME acceleration and non-thermal flare characteristics

We investigate the relationship between the main acceleration phase of coronal mass ejections (CMEs) and the particle acceleration in the associated flares as evidenced in RHESSI non-thermal X-rays for a set of 37 impulsive flare-CME events. CME peak velocity and peak acceleration yield distinct correlations with various parameters characterizing the flare-accelerated electron spectra. The highest correlation coefficient is obtained for the relation of the CME peak velocity and the total energy in accelerated electrons (c = 0.85), supporting the idea that the acceleration of the CME and the particle acceleration in the associated flare draw their energy from a common source, probably magnetic reconnection in the current sheet behind the erupting structure. In general, the CME peak velocity shows somewhat higher correlations with the non-thermal flare parameters than the CME peak acceleration, except for the spectral index of the accelerated electron spectrum which yields a higher correlation with the CME peak acceleration (c = -0.6), indicating that the hardness of the flare-accelerated electron spectrum is tightly coupled to the impulsive acceleration process of the rising CME structure. We also obtained high correlations between the CME initiation height $h_0$ and the non-thermal flare parameters, with the highest correlation of $h_0$ to the spectral index of flare-accelerated electrons (c = 0.8). This means that CMEs erupting at low coronal heights, i.e. in regions of stronger magnetic fields, are accompanied with flares which are more efficient to accelerate electrons to high energies. In the majority of events (80%), the non-thermal flare emission starts after the CME acceleration (6 min), giving a current sheet length at the onset of magnetic reconnection of 21 pm 7 Mm. The flare HXR peaks are well synchronized with the peak of the CME acceleration profile.