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| Paper: |
Small-scale Dynamo Action in Compressible Convection |
| Volume: |
429, Numerical Modeling of Space Plasma Flows, Astronum-2009 |
| Page: |
181 |
| Authors: |
Bushby, P. J.; Proctor, M. R. E.; Weiss, N. O. |
| Abstract: |
Motivated by observations of magnetic fields at the surface of the Sun, we
consider direct numerical simulations of dynamo action in
highly-stratified, three-dimensional compressible convection. Whether or
not a convective flow can drive a dynamo depends crucially upon the
magnetic Reynolds number. If this parameter is large enough that the
inductive effects of the fluid motions outweigh the dissipative effects of
magnetic diffusion, then dynamo action can occur. Simulating convection
with a Reynolds number of approximately 150, we find that it is
possible to excite a dynamo with computationally accessible values of the
magnetic Reynolds number. In the kinematic regime, the growth rate of the
dynamo has a logarithmic dependence upon the magnetic Reynolds
number. Following these dynamos into the nonlinear regime, we find that
intense, partially-evacuated concentrations of vertical magnetic flux form near
the upper surface of the computational domain. This partial evacuation
has a profound influence upon the efficiency of the
(explicit) numerical scheme that is used in these calculations. These
results can be related (in a qualitative sense) to recent
observations of magnetic fields in the quiet Sun. |
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