Buoyant Magnetic Loops Generated by Global Convective Dynamo Action
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Buoyant Magnetic Loops Generated by Global Convective Dynamo Action Nicholas J. Nelson · Benjamin P. Brown · A. Sacha Brun · Mark S. Miesch · Juri Toomre
Received: 10 October 2012 / Accepted: 25 December 2012 / Published online: 29 January 2013 © The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract Our global 3D simulations of convection and dynamo action in a Sun-like star reveal that persistent wreaths of strong magnetism can be built within the bulk of the convention zone. Here we examine the characteristics of buoyant magnetic structures that are self-consistently created by dynamo action and turbulent convective motions in a simulation with solar stratification but rotating at three times the current solar rate. These buoyant loops originate within sections of the magnetic wreaths in which turbulent flows amplify the fields to much higher values than is possible through laminar processes. These amplified portions can rise through the convective layer by a combination of magnetic buoyancy and advection by convective giant cells, forming buoyant loops. We measure statistical trends in the polarity, twist, and tilt of these loops. Loops are shown to preferentially arise in longitudinal patches somewhat reminiscent of active longitudes in the Sun, although broader in
Solar Origins of Space Weather and Space Climate Guest Editors: I. González Hernández, R. Komm, and A. Pevtsov N.J. Nelson · J. Toomre JILA and Dept. Astrophysical & Planetary Sciences, University of Colorado, Boulder, CO 80309-0440, USA N.J. Nelson e-mail: [email protected] B.P. Brown Dept. Astronomy, University of Wisconsin, Madison, WI 53706-1582, USA B.P. Brown Center for Magnetic Self Organization in Laboratory and Astrophysical Plasmas, University of Wisconsin, 1150 University Avenue, Madison, WI 53706, USA A. Sacha Brun Laboratoire AIM Paris-Saclay, CEA/Irfu Université Paris-Diderot CNRS/INSU, 91191 Gif-sur-Yvette, France M.S. Miesch () High Altitude Observatory, NCAR, Boulder, CO 80307-3000, USA e-mail: [email protected]
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extent. We show that the strength of the axisymmetric toroidal field is not a good predictor of the production rate for buoyant loops or the amount of magnetic flux in the loops that are produced. Keywords Convection zone · Global dynamo · Magnetic buoyancy · Flux emergence
1. Flux Emergence and Convective Dynamos Convective dynamo action in the interior of the Sun is the source of the magnetism that creates sunspots and drives space weather. This type of magnetism is not limited to the Sun, as magnetic activity is observed to be ubiquitous among Sun-like stars. To understand the origin of sunspots and starspots, one must explore the processes that generate magnetic structures and then transport them through the convection zone to the surface. Here we present the results of a global numerical simulation, called case S3, which self-consistently generates wreaths of strong magnetic field by dynamo action within the convective zone. Case S3 models the c
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