9 research outputs found
Solar dynamo model with nonlocal alpha-effect
The first results of the solar dynamo model that allows for the diamagnetic
effect of inhomogeneous turbulence and the nonlocal alpha-effect due to the
rise of magnetic loops are discussed. The nonlocal alpha-effect is not subject
to the catastrophic quenching related to the conservation of magnetic helicity.
Given the diamagnetic pumping, the magnetic fields are concentrated near the
base of the convection zone, although the distributed-type model covers the
entire thickness of the convection zone. The magnetic cycle period, the
equatorial symmetry of the field, its meridional drift, and the
polar-to-toroidal field ratio obtained in the model are in agreement with
observations. There is also some disagreement with observations pointing the
ways of improving the model.Comment: To appear in Astronomy Letters, 10 pages, 5 figure
Turbulent transport in hydromagnetic flows
The predictive power of mean-field theory is emphasized by comparing theory
with simulations under controlled conditions. The recently developed test-field
method is used to extract turbulent transport coefficients both in kinematic as
well as nonlinear and quasi-kinematic cases. A striking example of the
quasi-kinematic method is provided by magnetic buoyancy-driven flows that
produce an alpha effect and turbulent diffusion.Comment: 17 pages, 6 figures, topical issue of Physica Scripta on turbulent
mixing and beyon
The case for a distributed solar dynamo shaped by near-surface shear
Arguments for and against the widely accepted picture of a solar dynamo being
seated in the tachocline are reviewed and alternative ideas concerning dynamos
operating in the bulk of the convection zone, or perhaps even in the
near-surface shear layer, are discussed. Based on the angular velocities of
magnetic tracers it is argued that the observations are compatible with a
distributed dynamo that may be strongly shaped by the near-surface shear layer.
Direct simulations of dynamo action in a slab with turbulence and shear are
presented to discuss filling factor and tilt angles of bipolar regions in such
a model.Comment: 10 pages, 6 figures, Astrophys. J. 625 (scheduled for the 1 June 2005
issue