Astronomy and Astrophysics – Astronomy
Scientific paper
May 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.0502f&link_type=abstract
American Astronomical Society, 180th AAS Meeting, #05.02; Bulletin of the American Astronomical Society, Vol. 24, p.733
Astronomy and Astrophysics
Astronomy
Scientific paper
We study the dynamic evolution of emerging toroidal magnetic flux rings in the solar convective envelope by carrying out 3D numerical simulations based on the thin flux tube approximation of Spruit. We find: 1)For an axisymmetric flux ring, the aerodynamic drag force experienced by the ring when moving with respect to the ambient fluid transfers no angular momentum to the ring. Therefore in both cases, with or without the drag force, the ring moves nearly parallel to the rotational axis of the sun and emerges at a latitude significantly poleward of sunspot zones, as pointed out by Choudhuri and Gilman. However, for a non-axisymmetric flux ring (i.e. with wave-like undulations along its circumference), the aerodynamic drag force can transfer angular momentum to the flux ring, and therefore reduces the latitude of flux emergence to within the observed sunspot latitudes. 2)As each apex of a flux loop rises due to the magnetic buoyancy force, gas inside the flux tube tends to diverge from the apex. In the meantime, however, the Coriolis force drives a flow within the flux tube opposite to the direction of rotation. Thus the point of maximum divergence in the flow within the tube is shifted from the apex into the leading side (in the direction of rotation) of the emerging loop. The evacuation of plasma from the leading side of the loop results in a much lower internal gas pressure there as compared to that in the following side at the same depth. Therefore, the magnetic field strength is stronger on the leading side. The numerical simulations show that the field strength in the leading side of the loop can be twice as large as that of the following side at the same depth. This result offers a simple explanation for the observed fact that the leading polarity of an active region is more compact, forms sunspots more easily, and has a longer life time than does the following polarity.
DeLuca Edward E.
Fan Ying
Fisher George H.
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