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Session 35 - Solar Magnetic Fields.
Display session, Tuesday, June 11
Tripp Commons,

[35.02] A Possible Mechanism for the Origin Emerging Flux in the Sunspot Moat

J. Sakai (Toyama U.), R. Shine, A. Title (Lockheed Martin), M. Ryutova (Stanford U.)

Mass and energy flow near sunspots is associated with the emergence of magnetic flux which then moves outward in the sunspot moat. We present results of analytical and numerical studies of the interaction of horizontal magnetic flux and plasma flows in 3D-geometry. We show that nonlinear coupling of flux and plasma flows in the presence of a gravitational field lead to nonlinear dissipative instabilities which result in the formation of a solitary kink along the magnetic flux. The stability of a kink and its further evolution depends on the physical parameters of magnetic flux and surrounding medium. We discuss two major cases, magnetic soliton- and shock-like propagation along the magnetic flux, and specify the appropriate physical conditions for their realization. For example, under conditions in a sunspot moat, when the mass flow velocity exceeds about 0.5 v_A there occurs a magnetic soliton-like kink, propagating with a velocity less than the external mass flow velocity. The larger the radius of a flux tube, the larger the ``width'' of a soliton, and the lower the velocity of its propagation; the width of a soliton corresponds to the separation of ``legs'' of a kink which appear as magnetic field of the opposite polarities - the nearest to sunspot has obviously the same polarity. When the external mass flow velocity is less than about 0.5 v_A, a magnetic shock-like perturbation can propagate with a velocity larger than the external mass flow velocity. We apply these results to the observed properties of emerging flux and find reasonable qualitative and quantitative agreement.

This research was supported by NASA contract NAG5-3077 at Stanford University (M.R.) and NASA contract NAS8-39747 at

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