# 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 »

- Authors:

- School of Mathematics and Statistics, University of Glasgow—Glasgow G12 8QW (United Kingdom)
- NASA Ames Research Center—Moffett Field, CA 94035 (United States)
- 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}

}