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Sci Adv. 2016 Jul 13;2(7):e1600557. doi: 10.1126/sciadv.1600557. eCollection 2016 Jul.

A low upper limit on the subsurface rise speed of solar active regions.

Author information

1
Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany.
2
NorthWest Research Associates, 3380 Mitchell Lane, Boulder, CO 80301, USA.
3
Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany.; Institut für Astrophysik, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.; Center for Space Science, New York University Abu Dhabi, PO Box 129188 Abu Dhabi, UAE.; National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan.
4
Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany.; Institut für Astrophysik, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.
5
National Center for Atmospheric Research, High Altitude Observatory, 3080 Center Green Drive, Boulder, CO 80301, USA.

Abstract

Magnetic field emerges at the surface of the Sun as sunspots and active regions. This process generates a poloidal magnetic field from a rising toroidal flux tube; it is a crucial but poorly understood aspect of the solar dynamo. The emergence of magnetic field is also important because it is a key driver of solar activity. We show that measurements of horizontal flows at the solar surface around emerging active regions, in combination with numerical simulations of solar magnetoconvection, can constrain the subsurface rise speed of emerging magnetic flux. The observed flows imply that the rise speed of the magnetic field is no larger than 150 m/s at a depth of 20 Mm, that is, well below the prediction of the (standard) thin flux tube model but in the range expected for convective velocities at this depth. We conclude that convective flows control the dynamics of rising flux tubes in the upper layers of the Sun and cannot be neglected in models of flux emergence.

KEYWORDS:

Physics; astronomy; convection; solar physics

PMID:
27453947
PMCID:
PMC4956390
DOI:
10.1126/sciadv.1600557
[Indexed for MEDLINE]
Free PMC Article

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