Analysis of Coronal Mass Ejection Kinematics and Dependencies on Source Region Properties

Abstract

Coronal Mass Ejections (CMEs) are outbursts of coronal plasma bound in magnetic structures that are explosively accelerated. Their evolution into the heliosphere can be observed with coronagraphs and heliospheric imagers, which are able to detect the photospheric light scattered by the CME's plasma through Thomson scattering. Since CME's are optically thin, multi-viewpoint observations from space-borne coronagraphs are used to reconstruct their geometry and direction of propagation. CMEs originate from magnetic active regions (ARs), primarily of bipolar nature, which are observable in magnetograms of the photosphere and extreme ultraviolet images of the lower solar atmosphere. Often the eruption of a CME is accompanied by other sudden activity phenomena located in the same AR like solar flares, filament eruptions or post eruptive arcades. In this thesis a systematic investigation of the connection between the kinematics of CMEs and the properties of their corresponding source regions (SRs) is presented. For this purpose, a set of 21 Earth-directed CMEs between July 2011 and November 2012 was selected and analysed. The CME kinematics are obtained by applying a 3D modelling method, the Graduated Cylindrical Shell (GCS) model, to simultaneous multi-viewpoint observations taken with the SECCHI instrument suite onboard the twin STEREO spacecrafts and with the LASCO coronagraphs onboard the SOHO satellite. By using these instruments, the CME dynamics including the kinematics and geometry, are covered in high detail over a wide spatial range starting, for the majority of events, in the field of view (FOV) of EUVI below 2 solar radii and extending into the field of view of HI1 ~ 100 solar radii. An aerodynamic drag based propagation model, including distance depending models of the solar wind and the drag coefficient as well as the CME mass determined with the GCS model and Thomson scattering theory, is used to extrapolate the measured CME trajectory to larger heliospheric distances. The extrapolated solar wind and CME characteristics are compared with in-situ measurements at L1. Furthermore, the model results are used in a torus instability (TI) Lorentz force model to describe the initial acceleration phase. The CME SRs are identified by tracking the CME trajectories back onto the solar surface and searching for ARs and related activity phenomena within in a spatial window of less than ±25° in longitude and ±10° in latitude and a time window of ±8 hours to the first remote sensing observation. The ARs identified in this way as CME SRs are analysed for their magnetic and geometric properties in a time range ~ ±6 hours around the eruption time using the SMART code and line of sight magnetograms of SDO/HMI. The results show a very good agreement between the SR and initial CME geometry with a small shift in the SR latitude towards the solar equatorial plane with respect to the CME initial latitude. A highly dynamic behaviour, including deflections and rotations in the CME geometry within the first 20 solar radii, can be seen from the GCS modelling results. In the kinematic profiles, evidence for CME oscillations with periods between 29 and 93 min are found. Significant correlations are found between the CME SR magnetic flux as well as proxies of the free magnetic energy, which is provided by the CME SR, with the CME kinematic properties. The results of the drag model describe the measured CME trajectories with high accuracy and in general the predicted CME characteristics are in good agreement with the measurements in L1, while the TI Lorentz force model shows discrepancies to the observed CME accelerations.