EDP Sciences
Free access
Volume 390, Number 2, August I 2002
Page(s) 767 - 777
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20020711

A&A 390, 767-777 (2002)
DOI: 10.1051/0004-6361:20020711

Collapsing magnetic instability to solar intermittent flux and anomalous viscosity in accretion disks

X. Q. Li and H. Zhang

Department of Physics, Nanjing Normal University, Nanjing 210097, PR China

(Received 15 November 2001 / Accepted 24 April 2002)

It is shown that the transverse plasmon field is modulationally unstable in the Lyapunov sense, leading to a self-similar collapse of the magnetic flux. Such a collapsing magnetic instability is analyzed in both cases of magneto-hydrodynamics and kinetic plasma physics, with their applications to solar intermittent flux and anomalous viscosity in accretion disks, respectively. In the first case, we find that the equilibrium between the ponderomotive force and the Lorentz force in a current sheet gives rise to a more spatially intermittent collapsing magnetic flux, very similar to a turbulent pattern; as a result, the 0.1 kG flux cells with larger scales emerging at the surface from the solar interior become shredded and the flux is thereby contracted rather quickly to a small scale of the order of 100 km as well as concentrated into a 1-2 kG state. In the second case, based on Vlasov equations and Maxwell equations, the collapsing feature of the self-generated magnetic field from transverse plasmons is investigated on rather small scales of the motion or electric current in accretion disks; as the effects of the intermittent magnetic flux, an anomalous magnetic viscosity and an anomalous resistivity are indicated, with a different magnetic Prandtl number, which is not very sensitive to the temperature  T.

Key words: accretion: accretion disks -- magnetic fields -- Sun: magnetic fields

Offprint request: X. Q. Li, njxqli@jlonline.com

© ESO 2002