Magnetic Flux Emergence into the Solar Corona. III. The Role of Magnetic Helicity Conservation

2003 ◽  
Vol 584 (1) ◽  
pp. 479-496 ◽  
Author(s):  
M. Zhang ◽  
B. C. Low
Keyword(s):  
Magnetic Flux ◽  
Solar Corona ◽  
Magnetic Helicity ◽  
Flux Emergence ◽  
Helicity Conservation

Relation between the magnetic free energy and relative magnetic helicity in the MHD extreme state of solar corona

2020 ◽  
Author(s):  
Shangbin Yang ◽  
Joerg Buechner ◽  
Hongqi Zhang
Keyword(s):  
Magnetic Field ◽  
Free Energy ◽  
Solar Activity ◽  
Solar Corona ◽  
Solar Flares ◽  
Magnetic Helicity ◽  
Magnetic Free Energy ◽  
Helicity Conservation ◽  
Field Lines ◽  
Extreme State

<p>Magnetic helicity is a quantity describing the twist, writhe, and torsion of magnetic field lines and magnetic configurations . The concept of magnetic helicity has successfully been applied to characterize solar coronal processes. A conjecture about one approximation relation between free magnetic free energy and relative magnetic helicity in the MHD extreme state of solar corona has been proposed by using the concept of magnetic helicity conservation and Lie-Poisson mechanical structure of MHD. We use constant α force-free filed extrapolation to check out this relation. We also apply this relation to analyze the results from the simulations and observations. Such relation may be helpful to predict the solar activity like the solar flares and CMEs</p>

scholarly journals The Suppression and Promotion of Magnetic Flux Emergence in Fully Convective Stars

2016 ◽  
Vol 12 (S328) ◽  
pp. 85-92
Author(s):  
Maria A. Weber ◽  
Matthew K. Browning ◽  
Suzannah Boardman ◽  
Joshua Clarke ◽  
Samuel Pugsley ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Differential Rotation ◽  
Flux Emergence ◽  
Surface Magnetism ◽  
Flux Tubes ◽  
Cool Stars ◽  
M Dwarf ◽  
Insight Into ◽  
Individual Flux

AbstractEvidence of surface magnetism is now observed on an increasing number of cool stars. The detailed manner by which dynamo-generated magnetic fields giving rise to starspots traverse the convection zone still remains unclear. Some insight into this flux emergence mechanism has been gained by assuming bundles of magnetic field can be represented by idealized thin flux tubes (TFTs). Weber & Browning (2016) have recently investigated how individual flux tubes might evolve in a 0.3M⊙ M dwarf by effectively embedding TFTs in time-dependent flows representative of a fully convective star. We expand upon this work by initiating flux tubes at various depths in the upper ~50-75% of the star in order to sample the differing convective flow pattern and differential rotation across this region. Specifically, we comment on the role of differential rotation and time-varying flows in both the suppression and promotion of the magnetic flux emergence process.

scholarly journals ON THE ROLE OF REPETITIVE MAGNETIC RECONNECTIONS IN EVOLUTION OF MAGNETIC FLUX ROPES IN SOLAR CORONA

2016 ◽  
Vol 830 (2) ◽  
pp. 80 ◽  
Author(s):  
Sanjay Kumar ◽  
R. Bhattacharyya ◽  
Bhuwan Joshi ◽  
P. K. Smolarkiewicz
Keyword(s):  
Magnetic Flux ◽  
Solar Corona ◽  
Magnetic Flux Ropes ◽  
Flux Ropes

scholarly journals Interpreting magnetic helicity flux in solar flux emergence

2019 ◽  
Vol 85 (2) ◽  
Author(s):  
C. Prior ◽  
D. MacTaggart
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Solar Physics ◽  
Standard Form ◽  
Solar Flux ◽  
Magnetic Helicity ◽  
Flux Emergence ◽  
Topological Information ◽  
Solar Observations ◽  
Mhd Simulations

Magnetic helicity flux gives information about the topology of a magnetic field passing through a boundary. In solar physics applications, this boundary is the photosphere and magnetic helicity flux has become an important quantity in analysing magnetic fields emerging into the solar atmosphere. In this work we investigate the evolution of magnetic helicity flux in magnetohydrodynamic (MHD) simulations of solar flux emergence. We consider emerging magnetic fields with different topologies and investigate how the magnetic helicity flux patterns correspond to the dynamics of emergence. To investigate how the helicity input is connected to the emergence process, we consider two forms of the helicity flux. The first is the standard form giving topological information weighted by magnetic flux. The second form represents the net winding and can be interpreted as the standard helicity flux less the magnetic flux. Both quantities provide important and distinct information about the structure of the emerging field and these quantities differ significantly for mixed sign helicity fields. A novel aspect of this study is that we account for the varying morphology of the photosphere due to the motion of the dense plasma lifted into the chromosphere. Our results will prove useful for the interpretation of magnetic helicity flux maps in solar observations.

scholarly journals Nonequilibrium ionization and ambipolar diffusion in solar magnetic flux emergence processes

2020 ◽  
Vol 633 ◽  
pp. A66 ◽  
Author(s):  
D. Nóbrega-Siverio ◽  
F. Moreno-Insertis ◽  
J. Martínez-Sykora ◽  
M. Carlsson ◽  
M. Szydlarski
Keyword(s):  
Magnetic Flux ◽  
Ambipolar Diffusion ◽  
Solar Interior ◽  
Magnetized Plasma ◽  
Flux Emergence ◽  
Diffusion Term ◽  
Molecule Formation ◽  
Open Questions ◽  
The Impact

Context. Magnetic flux emergence from the solar interior has been shown to be a key mechanism for unleashing a wide variety of phenomena. However, there are still open questions concerning the rise of the magnetized plasma through the atmosphere, mainly in the chromosphere, where the plasma departs from local thermodynamic equilibrium (LTE) and is partially ionized. Aims. We aim to investigate the impact of the nonequilibrium (NEQ) ionization and recombination and molecule formation of hydrogen, as well as ambipolar diffusion, on the dynamics and thermodynamics of the flux emergence process. Methods. Using the radiation-magnetohydrodynamic Bifrost code, we performed 2.5D numerical experiments of magnetic flux emergence from the convection zone up to the corona. The experiments include the NEQ ionization and recombination of atomic hydrogen, the NEQ formation and dissociation of H2 molecules, and the ambipolar diffusion term of the generalized Ohm’s law. Results. Our experiments show that the LTE assumption substantially underestimates the ionization fraction in most of the emerged region, leading to an artificial increase in the ambipolar diffusion and, therefore, in the heating and temperatures as compared to those found when taking the NEQ effects on the hydrogen ion population into account. We see that LTE also overestimates the number density of H2 molecules within the emerged region, thus mistakenly magnifying the exothermic contribution of the H2 molecule formation to the thermal energy during the flux emergence process. We find that the ambipolar diffusion does not significantly affect the amount of total unsigned emerged magnetic flux, but it is important in the shocks that cross the emerged region, heating the plasma on characteristic times ranging from 0.1 to 100 s. We also briefly discuss the importance of including elements heavier than hydrogen in the equation of state so as not to overestimate the role of ambipolar diffusion in the atmosphere.

scholarly journals THE ROLE OF MAGNETIC HELICITY IN STRUCTURING THE SOLAR CORONA

2017 ◽  
Vol 835 (1) ◽  
pp. 85 ◽  
Author(s):  
K. J. Knizhnik ◽  
S. K. Antiochos ◽  
C. R. DeVore
Keyword(s):  
Solar Corona ◽  
Magnetic Helicity

scholarly journals Mean Field Dynamo Saturation: Toward Understanding Conflicting Results

2002 ◽  
Vol 12 ◽  
pp. 736-738
Author(s):  
Eric G. Blackman ◽  
George B. Field
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Magnetic Energy ◽  
Mean Field ◽  
Magnetic Helicity ◽  
Boundary Terms ◽  
Helicity Conservation ◽  
The Galaxy ◽  
Mean Field Dynamo

AbstractMean field dynamos may explain the origin of large scale magnetic fields of galaxies, but controversy arises over the extent of dynamo quenching by the growing field. Here we explain how apparently conflicting results may be mutually consistent, by showing the role of magnetic helicity conservation and boundary terms usually neglected. We estimate the associated magnetic energy flowing out of the Galaxy but emphasize that the mechanism of field escape needs to be addressed.

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