Fitting a 3-D analytic model of the coronal mass ejection to observations

We present the application of an analytic magnetohydrodynamic model (Gibson & Low 1998) to observations of the time-dependent expulsion of three-dimensional coronal mass ejections (CMEs) out of the solar corona. The model relates the white-light appearance of the CME to its internal magnetic field, which takes the form of a closed bubble, filled with a partly anchored, twisted magnetic flux rope and embedded in an otherwise open background field. The density distribution frozen into the expanding CME magnetic field is fully three-dimensional, and can be integrated along the line of sight to reproduce observations of scattered white light. The model is able to reproduce the three conspicuous features often associated with CMEs as observed with white-light coronagraphs: a surrounding high-density region, an internal low-density cavity, and a high-density core. The model also describes the self-similar radial expansion of these structures. By varying the model parameters we can fit the model directly to observations of CMEs. We are able to fit the size, shape, and velocity profile of CMEs observed by the SOHO/LASCO C2 and C3 coronagraphs and SOHO/EIT telescope. We also show how the model can quantitatively match the polarized Brightness (pB) contrast of a dark cavity emerging through the lower corona as observed by the HAO Manna Loa K-coronameter to within the noise level of the data. The model cannot reproduce non-self-similar features of observed CMEs. We consider the physical significance of such non-self-similar features.