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/s11214-016-0259-y

Cited by 16 publications

(10 citation statements)

References 170 publications

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“…Estimates for energy and helicity injections from the photosphere to the upper solar atmosphere in active regions are important for studying the dynamics of flux emergence (Cheung and Isobe, 2014;Liu et al, 2014), flux cancellation (Welsch, 2006;Yardley et al, 2018), and the evolution of active regions (van Driel-Gesztelyi and Green, 2015;Cheung et al, 2016). These estimates are also found to be particularly important for determining when and how solar eruptions, such as flares and coronal mass ejections (CMEs), occur in active regions (Cheung and DeRosa, 2012;Tziotziou, Georgoulis, and Liu, 2013;Kazachenko et al, 2015;Pariat et al, 2017;Pomoell, Lumme, and Kilpua, 2019).…”

Section: Introductionmentioning

confidence: 99%

Probing the Effect of Cadence on the Estimates of Photospheric Energy and Helicity Injections in Eruptive Active Region NOAA AR 11158

et al. 2019

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We study how the input-data cadence affects the photospheric energy and helicity injection estimates in eruptive NOAA Active Region 11158. We sample the novel 2.25-minute vector magnetogram and Dopplergram data from the Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) spacecraft to create input datasets of variable cadences ranging from 2.25 minutes to 24 hours. We employ state-of-the-art data processing, velocity, and electric-field inversion methods for deriving estimates of the energy and helicity injections from these datasets. We find that the electric-field inversion methods that reproduce the observed magnetic-field evolution through the use of Faraday's law are more stable against variable cadence: the PDFI (PTD-Doppler-FLCT-Ideal, where PTD refers to Poloidal-Toroidal Decomposition, and FLCT to Fourier Local Correlation Tracking) electric-field inversion method produces consistent injection estimates for cadences from 2.25 minutes up to two hours, implying that the photospheric processes acting on time scales below two hours contribute little to the injections, or that they are below the sensitivity of the input data and the PDFI method. On other hand, the electric-field estimate derived from the output of DAVE4VM (Differential Affine Velocity Estimator for Vector Magnetograms), which does not fulfill Faraday's law exactly, produces significant variations in the energy and helicity injection estimates in the 2.25 minutestwo hours cadence range. We also present a third, novel DAVE4VM-based electric-field estimate, which corrects the poor inductivity of the raw DAVE4VM estimate. This method is less sensitive to the changes of cadence, but it still faces significant issues for the lowest Electronic supplementary material The online version of this article (

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Section: Introductionmentioning

confidence: 99%

Probing the Effect of Cadence on the Estimates of Photospheric Energy and Helicity Injections in Eruptive Active Region NOAA AR 11158

et al. 2019

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“…Among them are a hydromagnetic instability related to quenching of eddy diffusivity by the enhanced magnetic field and cooling-down of the plasma (Kitchatinov & Mazur 2000), the already men-tioned NEMPI, and various MHD mechanisms of inductive excitation of magnetic fields strongly coupled with fluid motions (local dynamos; see, e.g., numerical simulations by Stein & Nordlund 2012, in which the initial presence of a uniform, untwisted, horizontal magnetic field is assumed). In particular, based on both observations and theory, Cheung et al (2017) note that the convective dynamo should operate in the convection zone over various spatial scales, without a clear separation between the large and small scales. We discussed some local formation mechanism for BMRs and sunspots in Paper I (and briefly in Paper II).…”

Section: Introductionmentioning

confidence: 99%

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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“…These host open magnetic field lines, while at low latitudes closed loops dominate. This relatively simple configuration is disrupted by strong concentrations of magnetic flux emerging through the photosphere at low latitudes, forming new active regions (ARs, van Driel-Gesztelyi and Green, 2015;Cheung et al, 2017). As magnetic flux emerges through the photosphere it starts out closed, but as the field strength increases the closed loops can reconnect with adjacent open field lines (van Driel-Gesztelyi et al, 2014;Ma et al, 2014;Kong et al, 2018), redistributing regions of existing open flux (Sheeley, Wang, and Harvey, 1989;Baker, van Driel-Gesztelyi, and Attrill, 2007) and in the process opening up previously closed flux (Wang and Sheeley, 2003a;Attrill et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Active Region Contributions to the Solar Wind over Multiple Solar Cycles

et al. 2021

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Both coronal holes and active regions are source regions of the solar wind. The distribution of these coronal structures across both space and time is well known, but it is unclear how much each source contributes to the solar wind. In this study we use photospheric magnetic field maps observed over the past four solar cycles to estimate what fraction of magnetic open solar flux is rooted in active regions, a proxy for the fraction of all solar wind originating in active regions. We find that the fractional contribution of active regions to the solar wind varies between 30% to 80% at any one time during solar maximum and is negligible at solar minimum, showing a strong correlation with sunspot number. While active regions are typically confined to latitudes ±30∘ in the corona, the solar wind they produce can reach latitudes up to ±60∘. Their fractional contribution to the solar wind also correlates with coronal mass ejection rate, and is highly variable, changing by ±20% on monthly timescales within individual solar maxima. We speculate that these variations could be driven by coronal mass ejections causing reconfigurations of the coronal magnetic field on sub-monthly timescales.

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The Life Cycle of Active Region Magnetic Fields

Cited by 16 publications

References 170 publications

Probing the Effect of Cadence on the Estimates of Photospheric Energy and Helicity Injections in Eruptive Active Region NOAA AR 11158

Probing the Effect of Cadence on the Estimates of Photospheric Energy and Helicity Injections in Eruptive Active Region NOAA AR 11158

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

Active Region Contributions to the Solar Wind over Multiple Solar Cycles

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