The Local and Global Expansion of Coronal Mass Ejections: Multi-spacecraft Measurements
Abstract
The radial expansion of coronal mass ejections (CMEs) is known to occur from remote observations, the variation of their properties with radial distance and from local in situ plasma measurements showing a decreasing speed profile throughout the magnetic ejecta. However, little is known on how local measurements compare to global measurements of expansion and whether radial expansion is mostly driven by the over-pressure of the magnetic ejecta or by the pressure-balanced expansion of the magnetic ejecta within the solar wind. Here, we take advantage of 40 CMEs being measured by two spacecraft in radial conjunction to determine how the magnetic field decrease with distance, as a measure of their global expansion. As all these CMEs are also measured in situ near 1 AU by STEREO or Wind, we are able to determine their local expansion from the speed decrease. We find that these two measures appear to have little relation with each other. We also determine the relation between measures of the CME expansion and the CME properties. We find that the expansion depends most strongly on the initial magnetic field strength inside the magnetic ejecta, but not significantly on its magnetic field measured near 1 AU. This is an indirect evidence that CME expansion in the innermost heliosphere is driven by over-expansion due to the high magnetic pressure inside the CME, while by the time the CMEs reach 1 AU, they are expanding due to the decrease in the solar wind dynamic pressure with distance.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSH33B3394L
- Keywords:
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- 7509 Corona;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7513 Coronal mass ejections;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7524 Magnetic fields;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7959 Models;
- SPACE WEATHER