Bibcode
Hood, A. W.; Archontis, V.; Galsgaard, K.; Moreno-Insertis, F.
Bibliographical reference
Astronomy and Astrophysics, Volume 503, Issue 3, 2009, pp.999-1011
Advertised on:
9
2009
Journal
Citations
67
Refereed citations
63
Description
Context: Models of flux emergence frequently use a twisted cylindrical
loop as the initial starting configuration and ignore the coupling
between the radiation field and plasma. In these models, the axis of the
original tube never emerges through the photosphere. Without the axis
emerging, it is very difficult to form a realistic sunspot. Aims:
The aim is to use a toroidal flux loop, placed beneath the solar
photosphere and study whether the axis of the system emerges fully into
the atmosphere. The toroidal curvature means that the plasma can drain
more effectively than in a straight cylindrical tube. Methods:
Three-dimensional magnetohydrodynamic numerical simulations of an
emerging magnetic flux tube are presented for an initial toroidal loop
model. The simulations use a Lagrangian-Remap code that is particularly
suited to dealing with shocks and strong current sheets. Results:
The evolution of the toroidal loop is followed and the characteristics
of the emergence process are compared with the traditional cylindrical
loops. The flux sources seen at the photosphere are more circular, and
there are less shearing motions in the upper photosphere. When the
initial magnetic field strength is relatively weak the evolution of the
system is similar to the cylindrical loop case, with the formation of a
new flux rope above the photosphere. A striking result is that for large
values of field strength the axial field of the toroidal loop emerges
fully into the corona. This is reported for the first time in
experiments of flux emergence in a highly stratified atmosphere that do
not solve self-consistently the radiation transfer problem. In addition,
the new flux rope forms below the original axis of the toroidal tube
when the field strength is sufficiently strong.
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