Launching Process of Coronal Mass Ejections

Details Launching Process of Coronal Mass Ejections Launching Process of Coronal Mass Ejections

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh41b1621s&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SH41B-1621

Physics

7509 Corona, 7513 Coronal Mass Ejections (2101), 7519 Flares, 7526 Magnetic Reconnection (2723, 7835), 7959 Models

Scientific paper

Coronal mass ejections (CMEs) are one the most spectacular explosive phenomena, in which large amount of mass and magnetic flux are ejected to the interplanetary space, as a result of a disruption of coronal magnetic field. It is very important for space weather science to understand the whole process of CMEs because of their close relation with geoeffective events. However, the physics of how and when CMEs are launched have not yet been understood. Although disruptions of coronal field (eruptions) are often observed as flares, in many cases, they are not accompanied by CMEs. The fact implies that occurrences of eruptions are not sufficient condition for CMEs and they are affected by some kinds of factor, for example, the interactions between magnetic field structure in an eruption and the ambient global scale magnetic field, such as confinement and reconnection. In order to examine the condition whether the eruption of coronal field can be launched as a CME, we performed a three-dimensional MHD simulation of a twisted flux rope ejected from a small and strong magnetic field active region surrounded by a global coronal magnetic field. We carried out the simulations for various configurations aiming to systematically reveal the condition for the capability of CME formation. As a result, we found, for example, that a flux rope cannot be ejected as a CME due to magnetic tension force of anchored field under weak surrounding field, while it can be ejected under moderately strong surrounding field. In the case with strong surrounding field, the significant amount of the magnetic flux inside of the ejecting flux rope reconnects with the ambient field and then the footpoint of the flux rope appears to move outward into weak field region. As the results, inward magnetic tension force of the large scale magnetic field become weak, while outward one becomes strong due to relaxation of the complex structure just after reconnection. The ejected flux rope shows tilting rotation in the direction perpendicular to the ejection line in the case where the CME is successfully formed. The tilting motion, which results from a relaxation of complex field structure, is much important for the determination of the field structure inside a propagating CME as well as for forecasting the orientation of magnetic field at the orbit of the Earth.

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