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

Toriumi, Shin; Hotta, Hideyuki

doi:10.3847/2041-8213/ab55e7

Cited by 45 publications

(49 citation statements)

References 45 publications

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“…The third one might be attributed to geometry of the emerging tube and how it couples with twist and the size of the flux tube, which has been discussed in Syntelis et al (2019). Finally, including realistic turbulent convection in the modeling can further yield a much more relaxed emergence process (Toriumi & Hotta 2019). In summary, our study shows that the photosphere field is very close to force-free during the emergence process, and this fact should be taken into consideration in future development of MHD simulations as well as the theories of flux emergence.…”

Section: Discussionmentioning

confidence: 97%

On the Lorentz Force and Torque of Solar Photospheric Emerging Magnetic Fields

Duan

Jiang

Toriumi

et al. 2020

ApJL

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Magnetic flux generated and intensified by the solar dynamo emerges into the solar atmosphere, forming active regions (ARs) including sunspots. Existing theories of flux emergence suggest that the magnetic flux can rise buoyantly through the convection zone but is trapped at the photosphere, while its further rising into the atmosphere resorts to the Parker buoyancy instability. To trigger such an instability, the Lorentz force in the photosphere needs to be as large as the gas pressure gradient to hold up an extra amount of mass against gravity. This naturally results in a strongly non-force-free photosphere, which is indeed shown in typical idealized numerical simulations of flux tube buoyancy from below the photosphere into the corona. Here we conduct a statistical study of the extents of normalized Lorentz forces and torques in the emerging photospheric magnetic field with a substantially large sample of Solar Dynamics Observatory/Helioseismic and Magnetic Imager vector magnetograms. We found that the photospheric field has a rather small Lorentz force and torque on average, and thus is very close to a force-free state, which is not consistent with theories as well as idealized simulations of flux emergence. Furthermore, the small extents of forces and torques seem not to be influenced by the emerging AR's size, the emergence rate, or the nonpotentiality of the field. This result puts an important constraint on future development of theories and simulations of flux emergence.

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Section: Discussionmentioning

confidence: 97%

On the Lorentz Force and Torque of Solar Photospheric Emerging Magnetic Fields

Duan

Jiang

Toriumi

et al. 2020

ApJL

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“…We note that a significant number of flux-emergence simulations incorporated additional physics, such as convective motions, radiative heating and cooling, heat conduction, ambipolar diffusion, ion-neutral interactions, and non-equilibrium ionization (e.g., Leake and Arber, 2006;Stein and Nordlund, 2006;Cameron et al, 2007;Martínez-Sykora et al, 2008;Isobe et al, 2008;Cheung et al, 2010;Fang et al, 2010;Rempel and Cheung, 2014;Chen et al, 2017;Hansteen et al, 2017;Moreno-Insertis et al, 2018;Nóbrega-Siverio et al, 2018;Cheung et al, 2019;Toriumi and Hotta, 2019). These simulations are necessary for studying the thermodynamical aspects of phenomena related to flux emergence and the atmospheric response to the dynamic emergence of solar magnetic fields.…”

Section: Flux Emergence Modelingmentioning

confidence: 99%

Decoding the Pre-Eruptive Magnetic Field Configurations of Coronal Mass Ejections

et al. 2020

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A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emergence, flux cancellation, helicity condensation). Whether the CME culprit is an SMA or an MFR, however, has been strongly debated for thirty years. We formed an International Space Science Institute (ISSI) team to address and resolve this issue and report the outcome here. We review the status of the field across modeling and observations, identify the open and closed issues, compile lists of SMA and MFR observables to be tested against observations and outline research activities to close the gaps in our current understanding. We propose that the combination of multi-viewpoint multi-thermal coronal observations and multiheight vector magnetic field measurements is the optimal approach for resolving

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“…On the other hand, the discrepancy might result from errors in the vector magnetograms, since these errors can introduce spurious flows with the DAVE4VM code and thus influences our simulation. To elucidate this, we will test our model with error-free magnetograms from recent convective flux-emergence simulations [e.g., [38][39][40] as the ground-truth data.…”

Section: Discussionmentioning

confidence: 99%

MHD Modeling of Solar Coronal Magnetic Evolution Driven by Photospheric Flow

et al. 2021

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It is well-known that magnetic fields dominate the dynamics in the solar corona, and new generation of numerical modeling of the evolution of coronal magnetic fields, as featured with boundary conditions driven directly by observation data, are being developed. This paper describes a new approach of data-driven magnetohydrodynamic (MHD) simulation of solar active region (AR) magnetic field evolution, which is for the first time that a data-driven full-MHD model utilizes directly the photospheric velocity field from DAVE4VM. We constructed a well-established MHD equilibrium based on a single vector magnetogram by employing an MHD-relaxation approach with sufficiently small kinetic viscosity, and used this MHD equilibrium as the initial conditions for subsequent data-driven evolution. Then we derived the photospheric surface flows from a time series of observed magentograms based on the DAVE4VM method. The surface flows are finally inputted in time sequence to the bottom boundary of the MHD model to self-consistently update the magnetic field at every time step by solving directly the magnetic induction equation at the bottom boundary. We applied this data-driven model to study the magnetic field evolution of AR 12158 with SDO/HMI vector magnetograms. Our model reproduced a quasi-static stress of the field lines through mainly the rotational flow of the AR's leading sunspot, which makes the core field lines to form a coherent S shape consistent with the sigmoid structure as seen in the SDO/AIA images. The total magnetic energy obtained in the simulation matches closely the accumulated magnetic energy as calculated directly from the original vector magnetogram with the DAVE4VM derived flow field. Such a data-driven model will be used to study how the coronal field, as driven by the slow photospheric motions, reaches a unstable state and runs into eruptions.

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

Cited by 45 publications

References 45 publications

On the Lorentz Force and Torque of Solar Photospheric Emerging Magnetic Fields

On the Lorentz Force and Torque of Solar Photospheric Emerging Magnetic Fields

Decoding the Pre-Eruptive Magnetic Field Configurations of Coronal Mass Ejections

MHD Modeling of Solar Coronal Magnetic Evolution Driven by Photospheric Flow

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