DYNAMO EFFECTS NEAR THE TRANSITION FROM SOLAR TO ANTI-SOLAR DIFFERENTIAL ROTATION

ABSTRACT Numerical MHD simulations play an increasingly important role for understanding the mechanisms of stellar magnetism. We present simulations of convection and dynamos in density-stratified rotating spherical fluid shells. We employ a new 3D simulation code for obtaining the solution of a phy...

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Bibliographic Details
Published in:The Astrophysical journal 2015-09, Vol.810 (1), p.1-16
Main Authors: Simitev, Radostin D., Kosovichev, Alexander G., Busse, Friedrich H.
Format: Article
Language:English
Subjects:
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Buoyancy
CHAOS THEORY
Computer simulation
COMPUTERIZED SIMULATION
CONCENTRATION RATIO
CONVECTION
CORIOLIS FORCE
DENSITY
Differential rotation
DIPOLES
dynamo
MAGNETIC FIELDS
MAGNETISM
MAGNETOHYDRODYNAMICS
magnetohydrodynamics (MHD)
Mathematical models
MATHEMATICAL SOLUTIONS
OSCILLATIONS
Polar regions
PRESSURE GRADIENTS
Rotating generators
ROTATION
SPACE
stars: magnetic field
SUN
Sun: magnetic fields
Sun: rotation
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Summary:ABSTRACT Numerical MHD simulations play an increasingly important role for understanding the mechanisms of stellar magnetism. We present simulations of convection and dynamos in density-stratified rotating spherical fluid shells. We employ a new 3D simulation code for obtaining the solution of a physically consistent anelastic model of the process with a minimum number of parameters. The reported dynamo simulations extend into a "buoyancy-dominated" regime where the buoyancy forcing is dominant while the Coriolis force is no longer balanced by pressure gradients, and strong anti-solar differential rotation develops as a result. We find that the self-generated magnetic fields, despite being relatively weak, are able to reverse the direction of differential rotation from anti-solar to solar-like. We also find that convection flows in this regime are significantly stronger in the polar regions than in the equatorial region, leading to non-oscillatory dipole-dominated dynamo solutions, and to a concentration of magnetic field in the polar regions. We observe that convection has a different morphology in the inner and the outer part of the convection zone simultaneously such that organized geostrophic convection columns are hidden below a near-surface layer of well-mixed highly chaotic convection. While we focus our attention on the buoyancy-dominated regime, we also demonstrate that conical differential rotation profiles and persistent regular dynamo oscillations can be obtained in the parameter space of the rotation-dominated regime even within this minimal model.
ISSN:0004-637X
1538-4357
1538-4357
DOI:10.1088/0004-637X/810/1/80