Kinematics of Two Eruptive Prominences observed by EUVI/STEREO

Two large northern polar crown prominences that erupted on 2010 April 13 and 2010 August 1 were analysed using images obtained from the Extreme UltraViolet Imager on the twin Solar Terrestrial Relations Observatory spacecraft. Several features along the prominence legs were reconstructed using a stereoscopic reconstruction technique developed by us. The three-dimensional changes exhibited by the prominences can be explained as an interplay between two different motions, namely helical twist in the prominence spine, and overall non-radial equatorward motion of the entire prominence structure. The sense of twist in both the prominences is determined from the changes in latitudes and longitudes of the reconstructed features. The prominences are observed starting from a few hours before the eruption. Increase in height before and during the eruption allowed us to study kinematics of the prominences in the two phases of eruption, the slow rise and the fast eruptive phase. A constant value of acceleration was found for each reconstructed feature in each phase, but it showed significant change from one leg to the other in both the prominences. The magnitude of acceleration during the eruptive phase is found to be commensurate with the net effect of the two motions stated above.