Distribution of magnetic energy in αΩ-dynamos, I: The method
作者:
J.H. G. M. Van Geffen,
P. Hoyng,
期刊:
Geophysical & Astrophysical Fluid Dynamics
(Taylor Available online 1993)
卷期:
Volume 71,
issue 1-4
页码: 187-221
ISSN:0309-1929
年代: 1993
DOI:10.1080/03091929308203602
出版商: Taylor & Francis Group
关键词: Dynamo processes;mean-field MHD;stochastic processes;turbulence;vorticity
数据来源: Taylor
摘要:
In this paper a method for solving the equation for the mean magnetic energy <BB> of a solar type dynamo with an axisymmetric convection zone geometry is developed and the main features of the method are described. This method is referred to as the finite magnetic energy method since it is based on the idea that the real magnetic fieldBof the dynamo remains finite only if <BB> remains finite. Ensemble averaging is used, which implies that fields of all spatial scales are included, small-scale as well as large-scale fields. The method yields an energy balance for the mean energy density ϵ ≡B2/8π of the dynamo, from which the relative energy production rates by the different dynamo processes can be inferred. An estimate for the r.m.s. field strength at the surface and at the base of the convection zone can be found by comparing the magnetic energy density and the outgoing flux at the surface with the observed values. We neglect resistive effects and present arguments indicating that this is a fair assumption for the solar convection zone. The model considerations and examples presented indicate that (1) the energy loss at the solar surface is almost instantaneous; (2) the convection in the convection zone takes place in the form of giant cells; (3) the r.m.s. field strength at the base of the solar convection zone is no more than a few hundred gauss; (4) the turbulent diffusion coefficient within the bulk of the convection zone is about 1014cm2s−1, which is an order of magnitude larger than usually adopted in solar mean field models.
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