Simulation of Magnetic Activity in the Sun: A Fast Dynamo
Stephen Childress
This film shows the growth of a magnetic field in a
time-dependent flow of an electrically conducting fluid of finite
small resistivity. The motion consisting of two periodically
varying Beltrami waves having the same "helicity". The flow in the
plane of the screen has the form of an eddy of closed streamlines
perturbed by a small time-varying component, but there is also
motion perpendicular to the plane of the screen. In the
lower-right-center of the screen one can see the build-up of field
field within a "heteroclinic tangle". Notice how the field
(positive red, negative blue) is amplified by being stretched and
folded within the lobes of the tangle. There is also a phase shift
due to the flow perpendicular to the screen, which causes the
folds, otherwise producing alternating bands of red and blue, hence
canceling magnetic flux, to "unmix" into coherent regions of blue
and red. During the time interval shown the magnetic field
increases by a factor of about 10,000.
This "dynamo action' is believed to occur in the convective
regions of the Sun's interior. There, dynamical effects of the
magnetic field act to modify the fluid flow in such a way that the
growth of the field is arrested at the levels observed over a solar
cycle. (Prepared by S. Childress and E. Wolfson, with thanks to
Dave Galloway for the code).
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