On the Expansion Speed of Coronal Mass Ejections: Implications for Self-Similar Evolution
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On the Expansion Speed of Coronal Mass Ejections: Implications for Self-Similar Evolution L.A. Balmaceda1,2 · A. Vourlidas3,4 · G. Stenborg5 · O.C. St. Cyr2,6
Received: 19 March 2020 / Accepted: 14 July 2020 © Springer Nature B.V. 2020
Abstract A proper characterization of the kinematics of coronal mass ejections (CMEs) is important not only for practical purposes, i.e. space weather forecasting, but also to improve our current understanding of the physics behind their evolution in the middle corona and into the heliosphere. The first and core step toward this goal is the estimation of the three main components of the CME speeds, namely the expansion speed relative to the center of motion in both, the radial and lateral directions, and the propagation speed (i.e. Vfront , Vlat , Vbulk , respectively). To this aim, we exploit the observations obtained with COR2 onboard the Solar Terrestrial Relations Observatory (STEREO) from 2007 to 2014 to investigate the relationships among the different components as a function of the heliocentric distance of the CME events. Here, we analyze a sample of 475 CMEs. The selected events exhibit clear flux rope signatures as seen either edge on (i.e. F-CMEs: three-part structure, presence of a cavity) or face on (i.e. L- or loop CMEs) in white light images. Our main findings are: i) L-CMEs show almost twice as large expansion speeds compared to F-CMEs (Vfront,L = 367 km s−1 , Vlat,L = 365 km s−1 vs. Vfront,F = 215 km s−1 , Vlat,F = 182 km s−1 ); ii) the relationship between the two components of the expansion speeds is linear and does not change with height; iii) the ratio of the propagation speed to the lateral expansion speed This article belongs to the Topical Collection: Towards Future Research on Space Weather Drivers Guest Editors: Hebe Cremades and Teresa Nieves-Chinchilla
B L.A. Balmaceda
[email protected] A. Vourlidas [email protected]
1
George Mason University, 4400 University Dr, Fairfax, VA 22030, USA
2
Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA
3
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
4
IAASARS, National Observatory of Athens, 15236, Penteli, Greece
5
Space Science Division, U.S. Naval Research Laboratory, Washington, DC 20375, USA
6
Universities Space Research Association, Columbia, MD 21046, USA
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is a function of the angular width that describes the self-similarity evolution of a CME; and iv) 65% of the CMEs exhibit a self-similar evolution at 10 solar radii, reaching 70% at 15 solar radii. Keywords Coronal mass ejections, propagation · Coronal mass ejections, expansion
1. Introduction Coronal Mass Ejections (CMEs) are a major manifestation of explosive energy release in our solar system. The study and understanding of their formation and evolution can lead to important physical insights in the processes of energy accumulation and release. Analysis of CME morphology and kinematics is of particular interest because the CME acceleration
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