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Building and maintaining a solar tachocline through convective dynamo action

Matilsky, Loren Isaac; Toomre, Juri

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Wolk, Scott

The dynamical maintenance of the Sun’s tachocline of rotational shear remains one of the outstanding mysteries of solar physics. We present a series of three-dimensional MHD anealastic simulations in rotating spherical shells that for the first time achieve a tachocline self-consistently, in which a dynamo operates within both the convection zone and underlying stable region. With the introduction of a small, random seed magnetic field to a hydrodynamic progenitor, the initially differentially rotating radiative interior is forced into solid-body rotation by a convectively excited dynamo, and afterward is maintained for centuries-long timescales. The overall result is similar in spirit to one of the “main contenders” for tachocline confinement—Gough and McIntyre (1998)—in which a primordial magnetic field stops the inward radiative spreading of the differential rotation. However, these new simulations using the Rayleigh code make no assumptions about the Sun’s fossil interior magnetic field. They thus offer a possibly more realistic magnetic confinement scenario for the tachocline that is here shown to be achieved by a fully nonlinear MHD convective dynamo operating in the solar interior.

Computational Resources for this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. Rayleigh has been developed by Nicholas Featherstone with support by the NSF through the Computational Infrastructure for Geodynamics (CIG). This effort was supported by NSF grants NSF-0949446 and NSF-1550901. See the referenced publications by Featherstone et al., Hindman et al., and Matsui et al. for more details. This work is funded by NASA grant 80NSSC18K1127.
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