Numerical Simulations of Flare-productive Active Regions: δ-sunspots, Sheared Polarity Inversion Lines, Energy Storage, and Predictions

Toriumi, Shin; Takasao, Shinsuke

doi:10.3847/1538-4357/aa95c2

Cited by 72 publications

(89 citation statements)

References 84 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…As shown above, the velocity shear of the counterstreaming flow, driven by the Lorentz force acting on each spot umbra (Section 3.2), intensifies the magnetic shear at the PIL. In the previous ideal δ-spot model by Toriumi & Takasao (2017) that lacks thermal convection, the horizontal field at the PIL was in fact intensified, but only up to an equipartition field strength of about 1 kG. In the present model, on the contrary, the vigorous convection continues around the PIL (δ-spot light bridge), which further strengthens the field to 4 kG.…”

Section: Magnetic Properties Of the δ-Spot Pilcontrasting

confidence: 58%

Spontaneous Generation of δ-sunspots in Convective Magnetohydrodynamic Simulation of Magnetic Flux Emergence

Toriumi

Hotta

2019

ApJL

Self Cite

View full text Add to dashboard Cite

Observations reveal that strong solar flares and coronal mass ejections tend to occur in complex active regions characterized by δ-sunspots, spot rotation, sheared polarity inversion lines (PILs), and magnetic flux ropes. Here we report on the first modeling of spontaneous δ-spot generation as a result of flux emergence from the turbulent convection zone. Utilizing state-of-the-art radiative magnetohydrodynamics code R2D2, we simulate the emergence of a force-free flux tube in the convection zone that stretches down to −140 Mm. Elevated by large-scale convective upflows, the tube appears on the photosphere as two emerging bipoles. The opposite polarities collide against each other due to the subsurface connectivity, and they develop into a pair of closely-packed δ-spots. The Lorentz force drives the spot rotation and a strong counter-streaming flow of 10 km s −1 at the PIL in δ-spots, which, in tandem with local convection, strengthens the horizontal field to 4 kG and builds up a highly-sheared PIL. In the atmosphere above the PIL, a flux rope structure is created. All these processes follow the multi-buoyant segment theory of the δ-spot formation, and they occur as a natural consequence of interaction between magnetic flux and turbulent convection, suggesting that the generation of δ-spots and the resultant flare eruptions may be a stochastically determined process.

show abstract

Section: Magnetic Properties Of the δ-Spot Pilcontrasting

confidence: 58%

Spontaneous Generation of δ-sunspots in Convective Magnetohydrodynamic Simulation of Magnetic Flux Emergence

Toriumi

Hotta

2019

ApJL

Self Cite

View full text Add to dashboard Cite

show abstract

“…In a recent simulation by Toriumi & Takasao (2017) the former two scenarios (Case 1 and 2) are reproduced in twice the spatial resolution (512 3 domain size) with the addition of two more scenarios. That is, a (linear) "Quadrupole" emergence (similar to Case 1), two flux tube emergence named as "inter-AR" emergence (but similar to Case 2), kink-unstable bipolar emergence referred to as "spot-spot" emergence, and parasitic bipole emergence called therein as "spot-satellite" emergence.…”

Section: Implications For Previous Emergence-based Data-inspired Modelsmentioning

confidence: 99%

The Origin of Major Solar Activity: Collisional Shearing between Nonconjugated Polarities of Multiple Bipoles Emerging within Active Regions

Chintzoglou

Zhang

Cheung

et al. 2019

ApJ

108

View full text Add to dashboard Cite

Active Regions (ARs) that exhibit compact Polarity Inversion Lines (PILs) are known to be very flare-productive. However, the physical mechanisms behind this statistical inference have not been demonstrated conclusively. We show that such PILs can occur due to the collision between two emerging flux tubes nested within the same AR. In such multipolar ARs, the flux tubes may emerge simultaneously or sequentially, each initially producing a bipolar magnetic region (BMR) at the surface. During each flux tube's emergence phase, the magnetic polarities can migrate such that opposite polarities belonging to different BMRs collide, resulting in shearing and cancellation of magnetic flux. We name this process "collisional shearing" to emphasize that the shearing and flux cancellation develops due to the collision. Collisional shearing is a process different from the known concept of flux cancellation occurring between polarities of a single bipole, a process that has been commonly used in many numerical models. High spatial and temporal resolution observations from the Solar Dynamics Observatory for two emerging ARs, AR11158 and AR12017, show the continuous cancellation of up to -2 -40% of the unsigned magnetic flux of the smallest BMR, which occurs at the collisional PIL for as long as the collision persists. The flux cancellation is accompanied by a succession of solar flares and CMEs, products of magnetic reconnection along the collisional PIL. Our results suggest that the quantification of magnetic cancellation driven by collisional shearing needs to be taken into consideration in order to improve the prediction of solar energetic events and space weather.

show abstract

“…The configuration of the magnetic field at and above the photosphere (e.g. bipolar or quadrupolar) will depend on the properties of the subphotospheric magnetic field [65][66][67][68][69]. The gradual emergence of the field at and above the solar surface leads to the self-consistent development of forces, which drive photospheric shearing and converging motions along a PIL [59,70] and rotation of the polarities [71][72][73].…”

Section: Numerical Simulations (A) Atmospheric Mfr Formationmentioning

confidence: 99%

The emergence of magnetic flux and its role on the onset of solar dynamic events

Archontis

Syntelis

2019

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

A plethora of solar dynamic events, such as the formation of active regions, the emission of jets and the occurrence of eruptions is often associated with the emergence of magnetic flux from the interior of the Sun to the surface and above. Here, we present a short review on the onset, driving and/or triggering of such events by magnetic flux emergence. We briefly describe some key observational examples, theoretical aspects and numerical simulations, towards revealing the mechanisms that govern solar dynamics and activity related to flux emergence. We show that the combination of important physical processes like shearing and reconnection of magnetic fieldlines in emerging flux regions or at their vicinity can power some of the most dynamic phenomena in the Sun on various temporal and spatial scales. Based on previous and recent observational and numerical studies, we highlight that, in most cases, none of these processes alone can drive and also trigger explosive phenomena releasing considerable amount of energy towards the outer solar atmosphere and space, such as flares, jets and large-scale eruptions (e.g. coronal mass ejections). In addition, one has to take into account the physical properties of the emerging field (e.g. strength, amount of flux, relative orientation to neighbouring and pre-existing magnetic fields, etc.) in order to better understand the exact role of magnetic flux emergence on the onset of solar dynamic events. This article is part of the theme issue ‘Solar eruptions and their space weather impact’.

show abstract

Numerical Simulations of Flare-productive Active Regions: δ-sunspots, Sheared Polarity Inversion Lines, Energy Storage, and Predictions

Cited by 72 publications

References 84 publications

Spontaneous Generation of δ-sunspots in Convective Magnetohydrodynamic Simulation of Magnetic Flux Emergence

Spontaneous Generation of δ-sunspots in Convective Magnetohydrodynamic Simulation of Magnetic Flux Emergence

The Origin of Major Solar Activity: Collisional Shearing between Nonconjugated Polarities of Multiple Bipoles Emerging within Active Regions

The emergence of magnetic flux and its role on the onset of solar dynamic events

Contact Info

Product

Resources

About