Propagation of Coronal Mass Ejections in the Inner Heliosphere

TL;DR

This paper presents a 3D reconstruction method for CME trajectories using STEREO data, revealing solar wind drag effects and capturing the first direct images of CME-driven shocks in interplanetary space.

Contribution

Developed a novel 3D reconstruction technique for CMEs with STEREO, enabling accurate kinematics and direct imaging of CME-driven shocks in interplanetary space.

Findings

Evidence of solar wind drag forces affecting CME speeds

First direct images of CME-driven shocks from 8 R_Sun to 120 R_Sun

Good agreement with empirical models of shock propagation

Abstract

Solar Coronal mass ejections (CMEs) are large-scale ejections of plasma and magnetic field from the corona, which propagate through interplanetary space. CMEs are the most significant drivers of adverse space weather on Earth, but the physics governing their propagation through the Heliosphere is not well understood. This is mainly due to the limited fields-of-view and plane-of-sky projected nature of previous observations. The Solar Terrestrial Relations Observatory (STEREO) mission launched in October 2006, was designed to overcome these limitations. In this thesis, a method for the full three dimensional (3D) reconstruction of the trajectories of CMEs using STEREO was developed. Using the 3D trajectories, the true kinematics were derived, which were free from projection effects. Evidence for solar wind (SW) drag forces acting in interplanetary space were found, with a fast CME decelerated and a slow CME accelerated toward typical SW velocities. It was also found that the fast CME showed a linear dependence on the velocity difference between the CME and the SW, while the slow CME showed a quadratic dependence. The differing forms of drag for the two CMEs indicated the forces responsible for their acceleration may have been different. CMEs are known to generate bow shocks as they propagate through the corona and SW. Although CME-driven shocks have previously been detected indirectly via their emission at radio frequencies, direct imaging has remained elusive due to their low contrast at optical wavelengths. Using STEREO observations, the first images of a CME-driven shock as it propagates through interplanetary space from 8 R_Sun to 120 R_Sun (0.5 AU) were captured. These observations were compared to empirically derived relation and in general showed good agreement.