On the dynamics of emerging toroidal magnetic flux tubes

Journal Article · Wed Jan 01 04:00:00 EST 1992 · American Astronomical Society, Bulletin; (United States)

OSTI ID:5720784

Fan, Y; Fisher, G H; Deluca, E E

In the present work the authors 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. They 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.

• OSTI ID: 5720784
• Journal Information: American Astronomical Society, Bulletin; (United States), Journal Name: American Astronomical Society, Bulletin; (United States) Vol. 24:2; ISSN 0002-7537; ISSN AASBAR
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANGULAR MOMENTUM
CORIOLIS FORCE
DRAG
MAGNETIC FLUX
MAIN SEQUENCE STARS
SIMULATION
SOLAR ACTIVITY
STARS
STARSPOTS
STELLAR ACTIVITY
SUN
SUNSPOTS
TORI