Statistics – Computation
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh22d..05n&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SH22D-05
Statistics
Computation
7513 Coronal Mass Ejections, 7519 Flares, 7524 Magnetic Fields, 7529 Photosphere
Scientific paper
We investigate whether the bulk of magnetic helicity carried away from the Sun by CMEs comes from photospheric horizontal shear motions or from emerging magnetic flux. Our study is focused on active region NOAA 9165 which is an ideal candidate for such study because (1) both new flux emergence and intense horizontal flows are observed during its short lifetime; (2) it shows rapid development and rapid decay and for a few days it is the site of violent activity; (3) the horizontal motions occur when it is close to disk center, thus minimizing the errors involved in the relevant computations; (4) observations of a magnetic cloud associated with one of the CMEs linked to the active region are available. The computed helicity change due to horizontal shear motions is probably the largest ever reported; it amounts to about the total helicity injected by the active region's differential rotation within more than 2 solar rotations. But the CMEs linked to the active region remove a factor of 8--64 more helicity than the helicity injected by horizontal shear motions. Consequently the main source of the helicity carried away by the CMEs is the new magnetic flux that emerges twisted from the convective zone. Our study implies that shear motions, even when they are strong, have little effect in the process of buildup of magnetic free energy that leads to the initiation of CMEs.
Nindos Alexander
Zhang Huazhong
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