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Title: 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 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 demonstratemore » 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.« less

Authors:
 [1];  [2];  [3]
  1. School of Mathematics and Statistics, University of Glasgow—Glasgow G12 8QW (United Kingdom)
  2. NASA Ames Research Center—Moffett Field, CA 94035 (United States)
  3. Department of Earth and Space Sciences, University of California, Los Angeles—Los Angeles, CA 90095 (United States)
Publication Date:
OSTI Identifier:
22525492
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 810; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CHAOS THEORY; COMPUTERIZED SIMULATION; CONCENTRATION RATIO; CONVECTION; CORIOLIS FORCE; DENSITY; DIPOLES; MAGNETIC FIELDS; MAGNETISM; MAGNETOHYDRODYNAMICS; MATHEMATICAL SOLUTIONS; OSCILLATIONS; PRESSURE GRADIENTS; ROTATION; SPACE; SUN

Citation Formats

Simitev, Radostin D., Kosovichev, Alexander G., and Busse, Friedrich H.. DYNAMO EFFECTS NEAR THE TRANSITION FROM SOLAR TO ANTI-SOLAR DIFFERENTIAL ROTATION. United States: N. p., 2015. Web. doi:10.1088/0004-637X/810/1/80.
Simitev, Radostin D., Kosovichev, Alexander G., & Busse, Friedrich H.. DYNAMO EFFECTS NEAR THE TRANSITION FROM SOLAR TO ANTI-SOLAR DIFFERENTIAL ROTATION. United States. doi:10.1088/0004-637X/810/1/80.
Simitev, Radostin D., Kosovichev, Alexander G., and Busse, Friedrich H.. Tue . "DYNAMO EFFECTS NEAR THE TRANSITION FROM SOLAR TO ANTI-SOLAR DIFFERENTIAL ROTATION". United States. doi:10.1088/0004-637X/810/1/80.
@article{osti_22525492,
title = {DYNAMO EFFECTS NEAR THE TRANSITION FROM SOLAR TO ANTI-SOLAR DIFFERENTIAL ROTATION},
author = {Simitev, Radostin D. and Kosovichev, Alexander G. and Busse, Friedrich H.},
abstractNote = {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.},
doi = {10.1088/0004-637X/810/1/80},
journal = {Astrophysical Journal},
number = 1,
volume = 810,
place = {United States},
year = {Tue Sep 01 00:00:00 EDT 2015},
month = {Tue Sep 01 00:00:00 EDT 2015}
}