Flux-tubes forming instability near the base of the rotating convection zone: A possible explanation for low latitudes of sunspots

Abstract

The rise of flux-tubes with intense magnetic fields from the base of the convection zone to the solar surface has been substantiated as a probable mechanism for sunspot formation. The origin of flux-tubes of sufficient strength (~10^5 G) is however uncertain. This paper considers the instability of a large-scale toroidal magnetic field caused by the magnetic suppression of convective heat transport as a candidate for the flux tube forming mechanism. The consideration employs the analytical dependence of the eddy diffusion on the magnetic field supplied by mean-field magnetohydrodynamics. The instability tends to produce regions of increased field strength with spatial scales of an order of 100 Mm at the base of the convection zone. Characteristic growth times of the instability are short compared to the 11-year cycle. The threshold field strength for the onset of the instability increases from several hundred Gauss in the vicinity of the equator to some kilo-Gauss at middle latitudes. Growth rates of unstable disturbances decrease with latitude. These latitudinal trends can be the reason for the observed confinement of sunspot activity to a near-equatorial belt.

arXiv commentAccepted in ApJ, 8 pages, 6 figures

References in corpus (11)

• Astrophysical magnetic fields and nonlinear dynamo theory
• Magnetic Wreaths and Cycles in Convective Dynamos
• The Rise of Active Region Flux Tubes in the Turbulent Solar Convective Envelope
• Turbulent magnetic Prandtl number and magnetic diffusivity quenching from simulations
• The solar magnetic field since 1700: I. Characteristics of sunspot group emergence and reconstruction of the butterfly diagram
• Meridional circulation in the solar convection zone: time-distance helioseismic inferences from four years of HMI/SDO observations
• Buoyant Magnetic Loops Generated by Global Convective Dynamo Action
• Solar meridional circulation from twenty-one years of SOHO/MDI and SDO/HMI observations: Helioseismic travel times and forward modeling in the ray approximation
• Helioseismic inversion to infer depth profile of solar meridional flow using spherical Born kernels
• Modeling the Rise of Fibril Magnetic Fields in Fully Convective Stars
• Large-Scale Magnetic Field Fragmentation in Flux-Tubes Near the Base of the Solar Convection Zone

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