Successful and Failed Flux Tube Emergence in the Solar Interior. (arXiv:1902.07969v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Syntelis_P/0/1/0/all/0/1">P. Syntelis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Archontis_V/0/1/0/all/0/1">V. Archontis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hood_A/0/1/0/all/0/1">A. Hood</a>
We report on our three-dimensional (3D) magnetohydrodynamic (MHD) simulations
of cylindrical weakly twisted flux tubes emerging from 18 Mm below the
photosphere. We perform a parametric study, by varying the initial magnetic
field strength ($B_0$), radius ($R$), twist ($alpha)$ and length of the
emerging part of the flux tube ($lambda$) to investigate how these parameters
affect the transfer of the magnetic field from the convection zone to the
photosphere. We show that the efficiency of emergence at the photosphere (i.e.
how strong the photospheric field will be in comparison to $B_0$) depends not
only on the $B_0$ but also the morphology of the emerging field and the twist.
We show that parameters such as $B_0$ and magnetic flux cannot alone determine
whether a flux tube will emerge to the solar surface. For instance, high-$B_0$
(weak-$B_0$) fields may fail (succeed) to emerge at the photosphere, depending
on their geometrical properties. We also show that the photospheric magnetic
field strength can vary greatly for flux tubes with the same $B_0$ but
different geometric properties. Moreover, in some cases we have found scaling
laws, whereby the magnetic field strength scales with the local density as
$Bpropto rho^kappa$, where $kappa approx 1$ deeper in the convection zone
and $kappa <1$, close to the photosphere. The transition between the two
values occurs approximately when the local pressure scale ($H_p$) becomes
comparable to the diameter of the flux tube ($H_papprox2R$). We derive forms
to explain how and when these scaling laws appear and compare them with the
numerical simulations.
We report on our three-dimensional (3D) magnetohydrodynamic (MHD) simulations
of cylindrical weakly twisted flux tubes emerging from 18 Mm below the
photosphere. We perform a parametric study, by varying the initial magnetic
field strength ($B_0$), radius ($R$), twist ($alpha)$ and length of the
emerging part of the flux tube ($lambda$) to investigate how these parameters
affect the transfer of the magnetic field from the convection zone to the
photosphere. We show that the efficiency of emergence at the photosphere (i.e.
how strong the photospheric field will be in comparison to $B_0$) depends not
only on the $B_0$ but also the morphology of the emerging field and the twist.
We show that parameters such as $B_0$ and magnetic flux cannot alone determine
whether a flux tube will emerge to the solar surface. For instance, high-$B_0$
(weak-$B_0$) fields may fail (succeed) to emerge at the photosphere, depending
on their geometrical properties. We also show that the photospheric magnetic
field strength can vary greatly for flux tubes with the same $B_0$ but
different geometric properties. Moreover, in some cases we have found scaling
laws, whereby the magnetic field strength scales with the local density as
$Bpropto rho^kappa$, where $kappa approx 1$ deeper in the convection zone
and $kappa <1$, close to the photosphere. The transition between the two
values occurs approximately when the local pressure scale ($H_p$) becomes
comparable to the diameter of the flux tube ($H_papprox2R$). We derive forms
to explain how and when these scaling laws appear and compare them with the
numerical simulations.
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