Confinement of the Solar Tachocline by a Non-Axisymmetric Dynamo. (arXiv:2311.10202v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Matilsky_L/0/1/0/all/0/1">Loren I. Matilsky</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brummell_N/0/1/0/all/0/1">Nicholas H. Brummell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hindman_B/0/1/0/all/0/1">Bradley W. Hindman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Toomre_J/0/1/0/all/0/1">Juri Toomre</a>
We recently presented the first 3D numerical simulation of the solar interior
for which tachocline confinement was achieved by a dynamo-generated magnetic
field. In this followup study, we analyze the degree of confinement as the
magnetic field strength changes (controlled by varying the magnetic Prandtl
number) in a coupled radiative zone (RZ) and convection zone (CZ) system. We
broadly find three solution regimes, corresponding to weak, medium, and strong
dynamo magnetic field strengths. In the weak-field regime, the large-scale
magnetic field is mostly axisymmetric with regular, periodic polarity reversals
(reminiscent of the observed solar cycle), but fails to create a confined
tachocline. In the strong-field regime, the large-scale field is mostly
non-axisymmetric with irregular, quasi-periodic polarity reversals, and creates
a confined tachocline. In the medium-field regime, the large-scale field
resembles a strong-field dynamo for extended intervals, but intermittently
weakens to allow temporary epochs of strong differential rotation. In all
regimes, the amplitude of poloidal field strength in the RZ is very well
explained by skin-depth arguments, wherein the oscillating field that gives
rise to the skin depth (in the medium- and strong-field cases) is a
non-axisymmetric field structure rotating with respect to the RZ. These new
simulations reaffirm that tachocline confinement by the solar dynamo (the
so-called fast magnetic confinement scenario) is possible, but suggest a new
picture in which non-axisymmetric field components rotating with respect to the
RZ play the primary role, instead of the regularly reversing axisymmetic field
associated with the 22-year cycle.
We recently presented the first 3D numerical simulation of the solar interior
for which tachocline confinement was achieved by a dynamo-generated magnetic
field. In this followup study, we analyze the degree of confinement as the
magnetic field strength changes (controlled by varying the magnetic Prandtl
number) in a coupled radiative zone (RZ) and convection zone (CZ) system. We
broadly find three solution regimes, corresponding to weak, medium, and strong
dynamo magnetic field strengths. In the weak-field regime, the large-scale
magnetic field is mostly axisymmetric with regular, periodic polarity reversals
(reminiscent of the observed solar cycle), but fails to create a confined
tachocline. In the strong-field regime, the large-scale field is mostly
non-axisymmetric with irregular, quasi-periodic polarity reversals, and creates
a confined tachocline. In the medium-field regime, the large-scale field
resembles a strong-field dynamo for extended intervals, but intermittently
weakens to allow temporary epochs of strong differential rotation. In all
regimes, the amplitude of poloidal field strength in the RZ is very well
explained by skin-depth arguments, wherein the oscillating field that gives
rise to the skin depth (in the medium- and strong-field cases) is a
non-axisymmetric field structure rotating with respect to the RZ. These new
simulations reaffirm that tachocline confinement by the solar dynamo (the
so-called fast magnetic confinement scenario) is possible, but suggest a new
picture in which non-axisymmetric field components rotating with respect to the
RZ play the primary role, instead of the regularly reversing axisymmetic field
associated with the 22-year cycle.
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