A Simple Technique for Identifying the Propagation Direction of CMEs in 3D Space

Abstract

By now several methods have been proposed enabling to determine the kinematic characteristics of coronal mass ejections (CMEs) in 3D space. Many of these methods are based on using the triangulation technique and stereoscopic observations of the CMEs with two and more spacecraft. As a rule, these methods involve relatively complicated procedures. Nevertheless, there is a need for a simple technique to find 3D characteristics of a CME motion fairly quickly. Such a technique, in particular, will enable to estimate on which side of the Sun (front side or back side for an observer on the Earth) the CME emerged, as well as to efficiently solve a problem relevant for solar-terrestrial physics: to determine the time of the CME arrival into Earth’s orbit. Such a simple technique is proposed in this article. The technique comprises two stages. First, one identifies the CME motion direction in the solar equatorial plane by using the data from any pair of the COR2 and LASCO (Large Angle and Spectrometric Coronagraph) C3 coronagraphs on board the Solar Terrestrial Relations Observatory (STEREO) A, B and the Solar and Heliospheric Observatory (SOHO), respectively. Next, one measures the angle between the CME motion direction in 3D space and the equatorial plane. We illustrate the technique for five CMEs that emerged either on the front side or back side of the Sun. An important advantage of the proposed technique is the possibility to quickly filter the events, that emerged on the front or back side of the Sun, by using only the information of the CME central position angle from a CME catalog. For the investigated CMEs, we obtained the time dependencies of the motion direction in the equatorial plane (angle $\varphi$), the angle between the CME motion direction in 3D space and the equatorial plane ($\lambda$), the distance from Sun’s center to the CME leading edge in 3D space ($R_{3D}$). For some investigated events, we compared our values for angle $\varphi$ and distance $R_{3D}$ with those obtained in other articles.