scholarly journals Spatial scales and locality of magnetic helicity

2020 ◽  
Vol 635 ◽  
pp. A95 ◽  
Author(s):  
C. Prior ◽  
G. Hawkes ◽  
M. A. Berger
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Spectral Methods ◽  
Wavelet Decomposition ◽  
Spatial Scales ◽  
Solar Interior ◽  
Magnetic Helicity ◽  
Clear Correlation ◽  
Arbitrary Boundary ◽  
The Magnetic Field

Context. Magnetic helicity is approximately conserved in resistive magnetohydrodynamic models. It quantifies the entanglement of the magnetic field within the plasma. The transport and removal of helicity is crucial in both dynamo development in the solar interior and active region evolution in the solar corona. This transport typically leads to highly inhomogeneous distributions of entanglement. Aims. There exists no consistent systematic means of decomposing helicity over varying spatial scales and in localised regions. Spectral helicity decompositions can be used in periodic domains and is fruitful for the analysis of homogeneous phenomena. This paper aims to develop methods for analysing the evolution of magnetic field topology in non-homogeneous systems. Methods. The method of multi-resolution wavelet decomposition is applied to the magnetic field. It is demonstrated how this decomposition can further be applied to various quantities associated with magnetic helicity, including the field line helicity. We use a geometrical definition of helicity, which allows these quantities to be calculated for fields with arbitrary boundary conditions. Results. It is shown that the multi-resolution decomposition of helicity has the crucial property of local additivity. We demonstrate a general linear energy-topology conservation law, which significantly generalises the two-point correlation decomposition used in the analysis of homogeneous turbulence and periodic fields. The localisation property of the wavelet representation is shown to characterise inhomogeneous distributions, which a Fourier representation cannot. Using an analytic representation of a resistive braided field relaxation, we demonstrate a clear correlation between the variations in energy at various length scales and the variations in helicity at the same spatial scales. Its application to helicity flows in a surface flux transport model show how various contributions to the global helicity input from active region field evolution and polar field development are naturally separated by this representation. Conclusions. The multi-resolution wavelet decomposition can be used to analyse the evolution of helicity in magnetic fields in a manner which is consistently additive. This method has the advantage over more established spectral methods in that it clearly characterises the inhomogeneous nature of helicity flows where spectral methods cannot. Further, its applicability in aperiodic models significantly increases the range of potential applications.

scholarly journals Magnetic Configuration and Evolution in a Solar Active Region

2001 ◽  
Vol 203 ◽  
pp. 294-296
Author(s):  
Y. Liu ◽  
H. Zhang
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Reconnection ◽  
Solar Atmosphere ◽  
Solar Active Region ◽  
Magnetic Configuration ◽  
Magnetic Helicity ◽  
Space Satellite ◽  
The Magnetic Field

We present results of the analysis of NOAA 8668, which was observed successively by space satellite (SOHO) and ground-based observatories (BBSO, Huairou). The combined observation offers us a good example of a region observed from low to high solar atmosphere. Several flares and a sigmoid filament were observed in the AR, and we observed the sigmoid filament from its birth to disintegration. The configuration of the magnetic field of the AR changed quickly as well as the loops. From EIT movies, we can even judge the sign of the sigmoid filament's magnetic helicity. The forming and heating of the loops were the result of magnetic reconnection, and the corona seemed heated when the loops became opened.

scholarly journals Evolution of relative magnetic helicity

2018 ◽  
Vol 613 ◽  
pp. A27 ◽  
Author(s):  
Shangbin Yang ◽  
Jörg Büchner ◽  
Jan Skála ◽  
Hongqi Zhang
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Solar Corona ◽  
Magnetic Reconnection ◽  
Interplanetary Space ◽  
New Method ◽  
Magnetic Clouds ◽  
Magnetic Helicity ◽  
Bottom Boundary ◽  
The Magnetic Field

Context. For a better understanding of the dynamics of the solar corona, it is important to analyse the evolution of the helicity of the magnetic field. Since the helicity cannot be directly determined by observations, we have recently proposed a method to calculate the relative magnetic helicity in a finite volume for a given magnetic field, which however required the flux to be balanced separately on all the sides of the considered volume. Aims. We developed a scheme to obtain the vector potential in a volume without the above restriction at the boundary. We studied the dissipation and escape of relative magnetic helicity from an active region. Methods. In order to allow finite magnetic fluxes through the boundaries, a Coulomb gauge was constructed that allows for global magnetic flux balance. The property of sinusoidal function was used to obtain the vector potentials at the 12 edges of the considered rectangular volume extending above an active region. We tested and verified our method in a theoretical fore-free magnetic field model. Results. We applied the new method to the former calculation data and found a difference of less than 1.2%. We also applied our method to the magnetic field above active region NOAA 11429 obtained by a new photospheric-data-driven magnetohydrodynamics (MHD) model code GOEMHD3. We analysed the magnetic helicity evolution in the solar corona using our new method. We find that the normalized magnetic helicity (H∕Φ2) is equal to −0.038 when fast magnetic reconnection is triggered. This value is comparable to the previous value (−0.029) in the MHD simulations when magnetic reconnection happened and the observed normalized magnetic helicity (−0.036) from the eruption of newly emerging active regions. We find that only 8% of the accumulated magnetic helicity is dissipated after it is injected through the bottom boundary. This is in accordance with the Woltjer conjecture. Only 2% of the magnetic helicity injected from the bottom boundary escapes through the corona. This is consistent with the observation of magnetic clouds, which could take magnetic helicity into the interplanetary space. In the case considered here, several halo coronal mass ejections (CMEs) and two X-class solar flares originate from this active region.

scholarly journals Study of helicity properties of peculiar active regions

2009 ◽  
Vol 5 (S264) ◽  
pp. 102-104 ◽  
Author(s):  
M. C. López Fuentes ◽  
C. H. Mandrini ◽  
P. Démoulin
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Active Regions ◽  
Solar Interior ◽  
Magnetic Helicity ◽  
Flux Tubes ◽  
Origin And Evolution ◽  
Magnetic Structures ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

AbstractPeculiar solar active regions (ARs), such as δ-islands and other high tilt bipoles, are commonly associated with the emergence of severely deformed magnetic flux tubes. Therefore, the study of these ARs provides valuable information on the origin and evolution of magnetic structures in the solar interior. Here, we infer the magnetic helicity properties of the flux tubes associated to a set of peculiar ARs by studying the evolution of photospheric magnetograms (SOHO/MDI) and coronal observations (SOHO/EIT and TRACE) in combination with force-free models of the magnetic field. We discuss how our results relate to different models of the evolution of emerging magnetic flux tubes.

scholarly journals Energetics of magnetic transients in a solar active region plage

2019 ◽  
Vol 623 ◽  
pp. A176 ◽  
Author(s):  
L. P. Chitta ◽  
A. R. C. Sukarmadji ◽  
L. Rouppe van der Voort ◽  
H. Peter
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Flux ◽  
Numerical Simulations ◽  
Extreme Ultraviolet ◽  
Spatial Scales ◽  
Coronal Loops ◽  
The Sun ◽  
Flux Emergence ◽  
Transient Events

Context. Densely packed coronal loops are rooted in photospheric plages in the vicinity of active regions on the Sun. The photospheric magnetic features underlying these plage areas are patches of mostly unidirectional magnetic field extending several arcsec on the solar surface. Aims. We aim to explore the transient nature of the magnetic field, its mixed-polarity characteristics, and the associated energetics in the active region plage using high spatial resolution observations and numerical simulations. Methods. We used photospheric Fe I 6173 Å spectropolarimetric observations of a decaying active region obtained from the Swedish 1-m Solar Telescope (SST). These data were inverted to retrieve the photospheric magnetic field underlying the plage as identified in the extreme-ultraviolet emission maps obtained from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). To obtain better insight into the evolution of extended unidirectional magnetic field patches on the Sun, we performed 3D radiation magnetohydrodynamic simulations of magnetoconvection using the MURaM code. Results. The observations show transient magnetic flux emergence and cancellation events within the extended predominantly unipolar patch on timescales of a few 100 s and on spatial scales comparable to granules. These transient events occur at the footpoints of active region plage loops. In one case the coronal response at the footpoints of these loops is clearly associated with the underlying transient. The numerical simulations also reveal similar magnetic flux emergence and cancellation events that extend to even smaller spatial and temporal scales. Individual simulated transient events transfer an energy flux in excess of 1 MW m−2 through the photosphere. Conclusions. We suggest that the magnetic transients could play an important role in the energetics of active region plage. Both in observations and simulations, the opposite-polarity magnetic field brought up by transient flux emergence cancels with the surrounding plage field. Magnetic reconnection associated with such transient events likely conduits magnetic energy to power the overlying chromosphere and coronal loops.

CHOICE OF CONDITIONS FOR MHD SIMULATIONS ABOVE THE ACTIVE REGION, ALLOWING THE STUDY OF THE SOLAR FLARE MECHANISM

2021 ◽  
Vol 44 ◽  
pp. 92-95
Author(s):  
A.I. Podgorny ◽  
◽  
I.M. Podgorny ◽  
A.V. Borisenko ◽  
N.S. Meshalkina ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Solar Flare ◽  
Magnetic Energy ◽  
Solar Radius ◽  
Computational Domain ◽  
Mhd Simulations ◽  
Flare Energy ◽  
Numerical Instabilities ◽  
The Magnetic Field

Primordial release of solar flare energy high in corona (at altitudes 1/40 - 1/20 of the solar radius) is explained by release of the magnetic energy of the current sheet. The observed manifestations of the flare are explained by the electrodynamical model of a solar flare proposed by I. M. Podgorny. To study the flare mechanism is necessary to perform MHD simulations above a real active region (AR). MHD simulation in the solar corona in the real scale of time can only be carried out thanks to parallel calculations using CUDA technology. Methods have been developed for stabilizing numerical instabilities that arise near the boundary of the computational domain. Methods are applicable for low viscosities in the main part of the domain, for which the flare energy is effectively accumulated near the singularities of the magnetic field. Singular lines of the magnetic field, near which the field can have a rather complex configuration, coincide or are located near the observed positions of the flare.

Modeling the magnetic structure of CMEs in the inner heliosphere based on data-driven time-dependent simulations of active region evolution

2021 ◽  
Author(s):  
Jens Pomoell ◽  
Emilia Kilpua ◽  
Daniel Price ◽  
Eleanna Asvestari ◽  
Ranadeep Sarkar ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Structure ◽  
Interplanetary Space ◽  
Coronal Magnetic Field ◽  
Time Dependent ◽  
Data Driven ◽  
Dependent Data ◽  
Heliospheric Physics ◽  
The Magnetic Field

<p>Characterizing the detailed structure of the magnetic field in the active corona is of crucial importance for determining the chain of events from the formation to the destabilisation and subsequent eruption and propagation of coronal structures in the heliosphere. A comprehensive methodology to address these dynamic processes is needed in order to advance our capabilities to predict the properties of coronal mass ejections (CMEs) in interplanetary space and thereby for increasing the accuracy of space weather predictions. A promising toolset to provide the key missing information on the magnetic structure of CMEs are time-dependent data-driven simulations of active region magnetic fields. This methodology permits self-consistent modeling of the evolution of the coronal magnetic field from the emergence of flux to the birth of the eruption and beyond. </p><p>In this presentation, we discuss our modeling efforts in which time-dependent data-driven coronal modeling together with heliospheric physics-based modeling are employed to study and characterize CMEs, in particular their magnetic structure, at various stages in their evolution from the Sun to Earth. </p>

scholarly journals Polarization and Position Measurements of Type III Bursts

1980 ◽  
Vol 86 ◽  
pp. 315-322 ◽  
Author(s):  
S. Suzuki ◽  
G.A. Dulk ◽  
K. V. Sheridan
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Open Field ◽  
Langmuir Waves ◽  
Type Iii ◽  
Brightness Temperatures ◽  
Polarization Characteristics ◽  
Field Lines ◽  
Cosine Law ◽  
The Magnetic Field

We report on the positional and polarization characteristics of Type III bursts in the range 24–220 MHz as measured by the Culgoora radioheliograph, spectrograph and spectropolarimeter. Our study includes 997 bursts which are of two classes: fundamental-harmonic (F-H) pairs and “structureless” bursts with no visible F-H structure. In a paper published elsewhere (Dulk and Suzuki, 1979) we give a detailed description and include observations of source sizes, heights and brightness temperatures. Here we concentrate on the polarization of the bursts and the variation of polarization from centre to limb. The observed centre-to-limb decrease in polarization approximately follows a cosine law. This decrease is not as predicted by simple theory but is consistent with other observations which imply that open field lines from an active region diverge strongly. The observed o-mode polarization of harmonic radiation implies that the wave vectors of Langmuir waves are always parallel, within about 20°, to the magnetic field, while the constancy of H polarization with frequency implies that the ratio fB/fP, the Alfvén speed vA and the plasma beta are constant with height on the open field lines above an active region. Finally, we infer that some factor, in addition to the magnetic field strength, controls the polarization of F radiation.

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