Murray, M. J.; Hood, A. W.; Moreno-Insertis, F.; Galsgaard, K.; Archontis, V.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 460, Issue 3, December IV 2006, pp.909-923
Fecha de publicación:
12
2006
Revista
Número de citas
101
Número de citas referidas
92
Descripción
Aims.We investigate the effects of varying the magnetic field strength
and the twist of a flux tube as it rises through the solar interior and
emerges into the atmosphere. Methods: .Using a 3D numerical MHD
code, we consider a simple stratified model, comprising of one solar
interior layer and three overlying atmospheric layers. We set a
horizontal, twisted flux tube in the lowest layer. The specific balance
of forces chosen results in the tube being fully buoyant and the
temperature is decreased in the ends of the tube to encourage the
formation of an Ω-shape along the tube's length. We vary the
magnetic field strength and twist independently of each other so as to
give clear results of the individual effects of each parameter.
Results: .We find a self-similar evolution in the rise and emergence of
the flux tube when the magnetic field strength of the tube is modified.
During the rise through the solar interior, the height of the crest and
axis, the velocity of the crest and axis, and the decrease in the
magnetic field strength of the axis of the tube are directly dependent
upon the initial magnetic field strength given to the tube. No such
self-similarity is evident when the twist of the flux tube is changed,
due to the complex interaction of the tension force on the rise of the
tube. For low magnetic field strength and twist values, we find that the
tube cannot fully emerge into the atmosphere once it reaches the top of
the interior since the buoyancy instability criterion cannot be
fulfilled. For those tubes that do advance into the atmosphere, when the
magnetic field strength has been modified, we find further self-similar
behaviour in the amount of tube flux transported into the atmosphere.
For the tubes that do emerge, the variation in the twist results in the
buoyancy instability, and subsequent emergence, occurring at different
locations along the tube's length.