First Determination of the True Mass of Coronal Mass Ejections: A Novel Approach to Using the Two STEREO Viewpoints

TL;DR

This paper introduces a new method to accurately determine the true mass and direction of coronal mass ejections (CMEs) by utilizing simultaneous observations from the two STEREO spacecraft, accounting for Thomson scattering effects.

Contribution

A novel approach that combines dual-viewpoint observations to directly measure the true mass and trajectory of CMEs, improving upon previous single-view methods.

Findings

Successfully derived the true mass of CMEs using the new method.

Demonstrated the importance of viewing geometry in CME mass estimation.

Provided a framework for future CME analysis with multiple viewpoints.

Abstract

The twin Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) COR2 coronagraphs of the Solar Terrestrial Relations Observatory (STEREO) provide images of the solar corona from two view points in the solar system. Since their launch in late 2006, the STEREO Ahead (A) and Behind (B) spacecrafts have been slowly separating from Earth at a rate of 22.5 degrees per year. By the end of 2007, the two spacecraft were separated by more than 40 degrees from each other. At this time, we began to see large-scale differences in the morphology and total intensity between coronal mass ejections (CMEs) observed with SECCHI-COR2 on STEREO-A and B. Due to the effects of the Thomson scattering geometry, the intensity of an observed CME is dependent on the angle it makes with the observed plane of the sky. From the intensity images, we can calculate the integrated line of sight electron density and mass. We demonstrate that is is possible to simultaneously derive the direction and true total mass of the CME if we make the simple assumption that the same mass should be observed in COR2-A and B.