Evolution of Coronal Cavity from Quiescent to Eruptive Phase in Association with Coronal Mass Ejection

The initiation mechanism of coronal mass ejections (CMEs) remains among the most elusive topics in solar physics. The initiation and triggering of CMEs can be studied by observing the coronal cavities in the lower coronal regions. These cavities appear as dark features and are believed to be the density depleted cross-sections of the magnetic flux ropes, where the magnetic field strength attains a much higher value compared to the background corona. Cavities may last for days or even weeks and evolve as the dark core part of the CME during the eruptive phase. In order to understand the pre-eruptive stability conditions for quiescent cavities and the triggering mechanisms for those structures to erupt, it is important to study the morphological evolution of the coronal cavities. In this work, we study the evolution of a cavity in lower corona using the observations from STEREO SECCHI/EUVI and PROBA2/SWAP EUV imager. In the quiescent phase, the cavity centroid height slowly rises from 1.10 to 1.23 R_S during its passage on the visible solar disc from May 30 to June 13, 2010 and its initial circular shaped morphology gradually expanded and evolved into elliptical shape prior to the eruption from the western solar limb. The extended field-of-view of SWAP fills the observational gap between 1 to 2 R_S . It enables us to capture the complete evolution of the erupting cavity starting from its EUV counterpart in the lower corona up to the white light cavity morphology seen in LASCO C2/C3 field-of-view. During the eruptive phase, we have observed a significant non-radial motion of the cavity at a very low coronal height of 1.3 R_S . Furthermore, the geometrical fitting to the cavity morphology in different time-steps during its eruptive phase reveals that it exhibits non-self similar expansion in the lower corona. We also discuss the role of the background magnetic field and the possible instabilities which may lead to the non-radial motion and initiation of the cavity eruption respectively.