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).

4Mbyte-mpeg movie