Distribution of magnetic energy in alpha-Omega-dynamos. III. A localized solar dynamo

Details Distribution of magnetic energy in alpha-Omega-dynamos. III. A localized solar dynamo Distribution of magnetic energy in alpha-Omega-dynamos. III. A localized solar dynamo

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...274..534v&link_type=abstract

Astronomy and Astrophysics, Vol. 274, p. 534 (1993)

Astronomy and Astrophysics

Astrophysics

5

Convection, Mhd, Stochastic Processes, Turbulence, Methods: Numerical, Sun: Activity, Sun: Magnetic Fields

Scientific paper

The finite magnetic energy method of Van Geffen & Hoyng (1992) is used to study a solar boundary layer dynamo. This method is based on the idea that the magnetic field B of the dynamo remains finite only if the mean magnetic energy remains finite. A localized dynamo is simulated by allowing the turbulent diffusion coefficient β to decrease towards the base of the convection zone, because the turbulence is less intense there. Such a dynamo operates with an r.m.s. field strength of about 10 G at the surface, and between 230 and 450 G at the base of the convection zone (depending on how much β decreases). This implies r.m.s. magnetic fluxes that are a factor of 10 to 100 too low to explain the fluxes observed in active regions on the solar surface. Furthermore, the localized dynamo appears to be very unstable: the damping time of the mean field , and hence the auto-correlation time of the field B, is only 14 to 18 days, so that the boundary layer dynamo simulated here is no more than a small-scale field dynamo which cannot sustain the solar cycle.