2D and 3D Kinematic Analysis of an Ideal-MHD Prominence Eruption

A range of ideal (for e.g. kink, torus) and non-ideal (for e.g. tether-cutting, breakout) MHD instabilities are thought to drive the eruption of prominences / filaments. The kinematic properties of eruptions can reveal the nature of the governing instability. Here we have carried out multi-dimensional kinematic analysis of a prominence eruption in order to characterise the respective roles of ideal-MHD instabilities throughout different phases of the eruption. Using SDO/AIA and STEREO/EUVI-A we reconstruct the leading edge of the prominence eruption in 3D, as observed between 26-Feb-2013 20:30:00 UT and 27-Feb-2013 05:45:00 UT. We use the reconstruction to measure the writhe of the prominence, and investigate the role of the kink instability during the slow-rise phase. We use a novel semi-automated, dual, edge detection method to precisely detect the leading edge and create height-time profiles from SDO/AIA image sequences in He II 30.4 nm, to analyse the kinematics of erupting plasma along radial slits intersecting the leading edge coordinates. With the height-time information for all points along the leading edge of the eruption, we fit the profiles using the parameterised height-time model function, h(t)=h(0)+vt+at^p, which corresponds to a linear (slow rise) phase followed by a non-linear (acceleration) phase. Through constraining the power index parameter, we investigate a series of fits of the eruption profile across all slits and identify the best fit in order to compare different eruption mechanisms. Importantly, we parameterise the onset time of the acceleration phase in order to confine the start time of the torus instability. Furthermore, we compare the height of the leading edge of the reconstruction to the critical decay index, as calculated from a PFSS model of the overlying field, to investigate the role of the torus instability during the acceleration phase. For the first time, our 3D kinematic analysis has identified a significant delay in the onset time of the acceleration phase together with a corresponding critical height at which acceleration starts to occur, as a function of position along the leading edge, which is in remarkable agreement with the determination of the critical height according to the decay index governing the torus instability.