2004/06/01 by Axel Brandenburg, Christer Sandin, Petri J. Käpylä
Biochemistry, Genetics and Molecular Biology · Engineering · Physics and Astronomy · #Fluid dynamics and aerodynamics studies #Geomagnetism and Paleomagnetism Studies #Solar and Space Plasma Dynamics #astro-ph
paper · pdf · doi:10.1017/s1743921304005101
published as IAU Symp. 223 (2004) 57-64 · 8 pages, 7 figs, IAU Symp. 223, In: Multi-Wavelength Investigations of Solar Activity. Eds: A.V. Stepanov, E.E. Benevolenskaya & A.G. Kosovichev
openalex publication_date 2004/06/01 · arxiv created 2004/07/29 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
The standard theory of the solar cycle in terms of an alpha-Omega dynamo hinges on a proper understanding of the nonlinear alpha effect. Boundary conditions play a surprisingly important role in determining the magnitude of alpha. For closed boundaries, the total magnetic helicity is conserved, and since the alpha effect produces magnetic helicity of one sign in the large scale field, it must simultaneously produce magnetic helicity of the opposite sign. It is this secondary magnetic helicity that suppresses the dynamo in a potentially catastrophic fashion. Open boundaries allow magnetic helicity to be lost. Simulations are presented that allow an estimate of alpha in the presence of open or closed boundaries, either with or without solar-like differential rotation. In all cases the sign of the magnetic helicity agrees with that observed at the solar surface (negative in the north, positive in the south), where significant amounts of magnetic helicity can be ejected via coronal mass ejections. It is shown that open boundaries tend to alleviate catastrophic alpha quenching. The importance of looking at current helicity instead of magnetic helicity is emphasized and the conceptual advantages are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstractservice.html