Photospheric Velocity Structures during the Emergence of Small Active Regions on the Sun

Khlystova, A. I.; Toriumi, Shin

doi:10.3847/1538-4357/aa688f

Cited by 8 publications

(5 citation statements)

References 49 publications

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“…On the other hand, magnetic fields of the active regions can be related to the emergence of global toroidal field fragments -flux-tubes -to the solar surface 1 . This picture is supported by observations of the active regions (see, e.g., Zwaan 1992;Lites et al 1998;Khlystova & Toriumi 2017). Modeling of buoyant fluxtubes reproduces the Joy's law for the active regions (D'Silva & Choudhuri 1993).…”

Section: Introductionsupporting

confidence: 60%

Large-Scale Magnetic Field Fragmentation in Flux-Tubes Near the Base of the Solar Convection Zone

Kitchatinov

2019

Astron. Lett.

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Magnetic quenching of turbulent thermal diffusivity leads to instability of the large-scale field with the production of spatially isolated regions of enhanced field. This conclusion follows from a linear stability analysis in the framework of mean-field magnetohydrodynamics that allows for thermal diffusivity dependence on the magnetic field. The characteristic growth time of the instability is short compared to the 11-year period of solar activity. The characteristic scale of the increased field regions measures in tens of mega-meters. The instability can produce magnetic inhomogeneities whose buoyant rise to the solar surface forms the solar active regions. The magnetic energy of the field concentrations coincides in order of magnitude with the energy of the active regions.

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Section: Introductionsupporting

confidence: 60%

Large-Scale Magnetic Field Fragmentation in Flux-Tubes Near the Base of the Solar Convection Zone

Kitchatinov

2019

Astron. Lett.

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“…where v th and j = ∇ × B are respectively the thermal velocity and the volume current density. The speed of the photospheric flow is generally accepted to be ∼1 km s −1 (Vekstein 2016;Khlystova & Toriumi 2017) and a straight forward calculation finds the thermal speed of the photospheric plasma to be also ∼1 km s −1 . Therefore, with v th ∼ v on the photosphere,…”

Section: A the Non-force-free Extrapolationmentioning

confidence: 99%

Successive Flux Rope Eruptions from δ-sunspots Region of NOAA 12673 and Associated X-class Eruptive Flares on 2017 September 6

Mitra

Joshi

Prasad

et al. 2018

ApJ

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In this paper, we present a multi-wavelength analysis of two X-class solar eruptive flares of classes X2.2 and X9.3 that occurred in the sigmoidal active region NOAA 12673 on 2017 September 6, by combining observations of Atmospheric Imaging Assembly and Helioseismic Magnetic Imager instruments on board the Solar Dynamics Observatory. On the day of the reported activity, the photospheric structure of the active region displayed a very complex network of δ-sunspots that gave rise to the formation of a coronal sigmoid observed in the hot EUV channels. Both X-class flares initiated from the core of the sigmoid sequentially within an interval of ∼3 hours and progressed as a single "sigmoid-to-arcade" event. Differential emission measure analysis reveals strong heating of plasma at the core of the active region right from the pre-flare phase which further intensified and spatially expanded during each event. The identification of a pre-existing magnetic null by non-force-free-field modeling of the coronal magnetic fields at the location of early flare brightenings and remote faint ribbon-like structures during the pre-flare phase, which were magnetically connected with the core region, provide support for the breakout model of solar eruption. The magnetic extrapolations also reveal flux rope structures prior to both flares which are subsequently supported by the observations of the eruption of hot EUV channels. The second X-class flare diverged from the standard flare scenario in the evolution of two sets of flare ribbons, that are spatially well separated, providing firm evidence of magnetic reconnections at two coronal heights.

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“…observationally detected signatures of HDFs prior to the magnetic-flux emergence. Khlystova & Toriumi (2017), using SOHO/MDI observations of the emergence of small AR 9021 and AR 10768, found strong upflows on a mesogranular scale at the initial stage of active-region formation. They noted good agreement in the time variation of the plasma-upflow velocity and area between these observations and numerical simulations of flux-tube emergence carried out by Toriumi et al (2011).…”

Section: Introductionmentioning

confidence: 98%

The Origin and Early Evolution of a Bipolar Magnetic Region in the Solar Photosphere

Гетлинг

Buchnev

2019

ApJ

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Finding the formation mechanisms for bipolar configurations of strong local magnetic field under control of the relatively weak global magnetic field of the Sun is a key problem of the physics of solar activity. This study is aimed at discriminating whether the magnetic field or fluid motion plays a primary, active role in this process. The very origin and early development stage of Active Region 12548 are investigated based on SDO/HMI observations of 2016 May 20-25. Full-vector magnetic and velocity fields are analyzed in parallel. The leading and trailing magnetic polarities are found to grow asymmetrically in terms of their amplitude, magnetic flux, and the time variation of these quantities. The leading-polarity magnetic element originates as a compact feature against the background of a distributed trailing-polarity field, with an already existing trailing-polarity magnetic element. No signs of strong horizontal magnetic fields are detected between the two magnetic poles. No predominant upflow between their future locations precedes the origin of this bipolar magnetic region (BMR); instead, upflows and downflows are mixed, with some prevalence of downflows. Any signs of a large-scale horizontal divergent flow from the area where the BMR develops are missing; in contrast, a normal supergranulation and mesogranulation pattern is preserved. This scenario of early BMR evolution is in strong contradiction with the expectations based on the model of a rising Ω-shaped loop of a flux tube of strong magnetic field, and an in situ mechanism of magnetic-field amplification and structuring should operate in this case.

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Photospheric Velocity Structures during the Emergence of Small Active Regions on the Sun

Cited by 8 publications

References 49 publications

Large-Scale Magnetic Field Fragmentation in Flux-Tubes Near the Base of the Solar Convection Zone

Large-Scale Magnetic Field Fragmentation in Flux-Tubes Near the Base of the Solar Convection Zone

Successive Flux Rope Eruptions from δ-sunspots Region of NOAA 12673 and Associated X-class Eruptive Flares on 2017 September 6

The Origin and Early Evolution of a Bipolar Magnetic Region in the Solar Photosphere

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