Magnetic geometry and dynamics of the fast coronal mass ejection of 1997 September 9

A coronal mass ejection (CME) was observed on 1997 September 9 by the Mauna Loa Solar Observatory Mark III K-coronameter (MK3) and by the LASCO C2/C3 and EIT instruments on board the SOHO spacecraft. Magnetograms and EIT images obtained on days leading up to the eruption show a neutral line that appears to correspond to the site of the eruption. Taken together, the data from these instruments provide a comprehensive, beginning-to-end record of the event within the 32 R. field of view. The motion of several features are tracked through the fields of view of MK3, C2, and C3. The CME exhibits the previously identified morphological features and dynamical properties consistent with those of an erupting magnetic flux rope with its legs connected to the Sun. The LASCO images and magnetograms indicate that the flux rope axis was aligned with the neutral line approximately 2 days behind the west limb. Its apparent orientation provides an oblique view of an erupting flux rope, a view that has not been discussed previously. A theoretical flux rope model is used to understand the forces responsible for the observed CME dynamics. Synthetic coronagraph images based on the model flux rope are constructed.