Astronomy and Astrophysics – Astronomy
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21640603o&link_type=abstract
American Astronomical Society, AAS Meeting #216, #406.03; Bulletin of the American Astronomical Society, Vol. 41, p.880
Astronomy and Astrophysics
Astronomy
Scientific paper
The structure of the magnetic field of the ejecta of a coronal mass ejection (CME) is not well known near the Sun. We propose using the subsonic plasma flows in the CME-sheath to constrain the CME field direction. We draw an analogy to the outer heliosphere, where Opher et al. (2009) used Voyager 2 measurements of the solar wind in the heliosheath to constrain the strength and direction of the local interstellar magnetic field. We simulate three ejections in a realistic background in the solar minimum conditions of 1997 May with the Space Weather Modeling Framework. Each ejection has the same initial energy, but a different magnetic field orientation in relation to the overall orientation of the active region field. We show that the sheath flows are sensitive to the direction of the initial magnetic field, and differ by more than 60 degrees when the CME-driven shock is located at 4.5 solar radii. Unlike the heliosheath flows, the CME-sheath flows are affected not only by the initial ejecta orientation but by the CME's evolution in the lower corona as well. We show that the evolutions differ because of the locations and intensities of reconnection events. We distinguish between the initial reconnection between the ejecta and the overlying field of the active region, and further reconnection events with the global solar coronal field (which occur beyond 2 solar radii). This late reconnection causes bulk motion and heating in the ejecta and sheaths, which affects the size of the CME-pause and the velocity profile of the CME. We suggest identifying the orientation of the magnetic field ejecta through velocity profiles in the lower corona and in situ CME-sheath flow measurements. These results provide new diagnostics to identify different initial CME magnetic field orientations without need for direct measurement.
Evans Martin R.
Opher Merav
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