The Life Cycle of Active Region Magnetic Fields

Cheung, Mark C. M.; Driel‐Gesztelyi, L. van; Pillet, V. Martı́nez; Thompson, M. J.

doi:10.1007/978-94-024-1521-6_11

Cited by 2 publications

(2 citation statements)

References 172 publications

(186 reference statements)

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“…14). There is no need to insert sub-photospheric flux ropes in the simulation box as done earlier, because recent 3-D MHD simulations added the evolution of realistic magneto-convection as a time-dependent boundary to drive the flux emergence process (Cheung and Isobe 2014;Cheung et al 2017). The fact that susnpots always appear within a time scale comparable to the flux emergence time of an active region, providing magnetic flux to the sunspot, indicates that coherent magnetic structures self-organize deep in the convection zone.…”

Section: Magnetic Field Self-organizationmentioning

confidence: 99%

Order out of Randomness: Self-Organization Processes in Astrophysics

Aschwanden¹,

Scholkmann²,

Béthune³

et al. 2018

Space Sci Rev

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Self-organization is a property of dissipative nonlinear processes that are governed by a global driving force and a local positive feedback mechanism, which creates regular geometric and/or temporal patterns, and decreases the entropy locally, in contrast to random processes. Here we investigate for the first time a comprehensive number of (17) self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous "order out of randomness", during the evolution from an initially disordered system to an ordered quasi-stationary system, mostly by quasi-periodic limit-cycle dynamics, but also by harmonic (mechanical or gyromagnetic) resonances. The global driving force can be due to gravity, electromagnetic forces, mechanical forces (e.g., rotation or differential rotation), thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational (Balbus-Hawley) instability, the convective (Rayleigh-Bénard) instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or a loss-cone instability. Physical models of astrophysical self-organization processes require hydrodynamic, magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical formulations of self-organizing systems generally involve coupled differential equations with limit-cycle solutions of the Lotka-Volterra or Hopf-bifurcation type.

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Section: Magnetic Field Self-organizationmentioning

confidence: 99%

Order out of Randomness: Self-Organization Processes in Astrophysics

Aschwanden¹,

Scholkmann²,

Béthune³

et al. 2018

Space Sci Rev

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“…This figure from Cheung et al () illustrates the relationships between (left) sunspots seen in the visible disk image, (center) the magnetic field strengths and polarities seen with a magnetograph (shown in gray scale with black and white the strongest inward and outward fields), and (right) the extreme ultraviolet image showing coronal loops over the strongest field regions. Note that not all magnetic features show up as sunspots.…”

Section: Introductionmentioning

confidence: 99%

The Solar Clock

Russell

Jian

Luhmann

2019

Reviews of Geophysics

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The Sun is powered by a very stable source of fusion energy in its core that radiates that energy outward in a constant flow. Yet it has a cycle of magnetic dynamo activity whose strength and duration are variable. This variability, which affects the Earth's “space climate,” points to temporal changes in the convective and diffusive transport of magnetic flux above the tachocline, where the flux is generated. The longest record we have of this variability is the time series of sunspot numbers. This record suggests that the interior of the Sun follows a clock‐like magnetic flux production cycle with a length of close to 11.05 years. The variations in sunspot cycle duration, as well as the sunspot number rise and fall times, their hemispheric asymmetries, and the maximum sunspot numbers of the individual cycles are likely produced in the process of the magnetic flux transport. Helioseismology continues to shed more light on the convection zone variabilities, including the “torsional oscillations” that seem to have a special connection to the emerging strong magnetic fluxes that produce the sunspots. These new observations may eventually lead to an explanation for the surprisingly good correlation between the rate of sunspot appearance and the maximum sunspot number and to a better understanding of the relationship between the solar dynamo and the sunspot number cycle. Better understanding of the polar regions awaits long‐term monitoring with a polar solar mission. Better predictions of near‐term space weather could be obtained from a permanent L5 monitor.

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The Life Cycle of Active Region Magnetic Fields

Cited by 2 publications

References 172 publications

Order out of Randomness: Self-Organization Processes in Astrophysics

Order out of Randomness: Self-Organization Processes in Astrophysics

The Solar Clock

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