How to Reach Superequipartition Field Strengths in Solar Magnetic Flux Tubes |
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| Authors: | A Ferriz-Mas O Steiner |
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| Institution: | 1.Departamento de Física Aplicada,Universidad de Vigo,Orense,Spain;2.Astronomy Division, Faculty of Physical Sciences,University of Oulu,Oulu,Finland;3.Kiepenheuer-Institut für Sonnenphysik,Freiburg,Germany |
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| Abstract: | A number of independent arguments indicate that the toroidal flux system responsible for the sunspot cycle is stored at the
base of the convection zone in the form of flux tubes with field strength close to 105 G. Although the evidence for such strong fields is quite compelling, how such field strength can be reached is still a topic
of debate. Flux expulsion by convection should lead to about the equipartition field strength, but the magnetic energy density
of a 105-G field is two orders of magnitude larger than the mean kinetic energy density of convective motions. Line stretching by
differential rotation (i.e., the “Ω effect” in the classical mean-field dynamo approach) probably plays an important role, but arguments based on energy considerations show that it does not seem feasible
that a 105-G field can be produced in this way. An alternative scenario for the intensification of the toroidal flux system in the overshoot
layer is related to the explosion of rising, buoyantly unstable magnetic flux tubes, which opens a complementary mechanism for magnetic-field intensification.
A parallelism is pointed out with the mechanism of “convective collapse” for the intensification of photospheric magnetic
flux tubes up to field strengths well above equipartition; both mechanisms, which are fundamentally thermal processes, are
reviewed. |
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| Keywords: | Sun: magnetic field Sun: flux tubes Sun: convection zone |
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