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Title:
Doubly Helical Coronal Ejections from Dynamos and Their Role in Sustaining the Solar Cycle
Authors:
Blackman, Eric G.; Brandenburg, Axel
Affiliation:
AA(Department of Physics and Astronomy and Laboratory for Laser Energetics, University of Rochester, Rochester, NY 14627.), AB(Nordita, Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark.)
Publication:
The Astrophysical Journal, Volume 584, Issue 2, pp. L99-L102. (ApJL Homepage)
Publication Date:
02/2003
Origin:
UCP
Astronomy Keywords:
Magnetic Fields, Magnetohydrodynamics: MHD, Stars: Magnetic Fields, Sun: Coronal Mass Ejections (CMEs), Sun: Magnetic Fields, Turbulence
DOI:
10.1086/368374
Bibliographic Code:
2003ApJ...584L..99B

Abstract

Two questions about the solar magnetic field might be answered together once their connection is identified. The first is important for large-scale dynamo theory: what prevents the magnetic back-reaction forces from shutting down the dynamo cycle? The second question is, what determines the handedness of twist and writhe in magnetized coronal ejecta? Magnetic helicity conservation is important for answering both questions. Conservation implies that dynamo generation of large-scale writhed structures is accompanied by the oppositely signed twist along these structures. The latter is associated with the back-reaction force. We suggest that coronal mass ejections simultaneously liberate small-scale twist and large-scale writhe of opposite sign, helping to prevent the cycle from quenching and enabling a net magnetic flux change in each hemisphere. Solar observations and helicity spectrum measurements from our simulation of a rising flux tube support this idea. We show a new pictorial of dynamo flux generation that includes the back-reaction and magnetic helicity conservation and represents the field by a ribbon or tube rather than a line.
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