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.