Partial Torus Instability in Initiating Coronal Mass Ejections

We have been studying the balance between internal and external Lorenz forces of an idealized flux rope and the role of the external overlying (strapping) magnetic field in triggering the torus instability. It has been theorized that the flux rope is the magnetic configuration of an erupting coronal mass ejection. The role of the overlying field is to maintain the flux rope in equilibrium, but it may eventually become unstable and erupt as the flux rope gradually rises up. We analyze the semi-circular flux rope model as proposed by Chen and others, which pre-supposes the existence of a flux rope in the corona. It is found that this model predicts a critical index of the overlying field that dictates the stability of the flux rope. This index is a function of the arc length of the loop, and we argue that this function is a generalized form of the torus instability. We have coined our finding the partial torus instability. We continue the research by looking for observational evidences of this instability. We use observations from SOHO, STEREO, and SDO, and compare the kinematics of eruptive prominences with extrapolated corona magnetic fields. Our comprehensive results of this study will be presented.