scholarly journals Tests and applications of nonlinear force-free field extrapolations in spherical geometry

2012 ◽  
Vol 8 (S294) ◽  
pp. 553-554
Author(s):  
Y. Guo ◽  
M. D. Ding
Keyword(s):  
Magnetic Field ◽  
Analytical Solution ◽  
Large Scale ◽  
Initial Conditions ◽  
Free Field ◽  
Spherical Geometry ◽  
Source Surface ◽  
Field Source ◽  
Nonlinear Force ◽  
Force Free Field

AbstractWe test a nonlinear force-free field (NLFFF) optimization code in spherical geometry with an analytical solution from Low and Lou. The potential field source surface (PFSS) model is served as the initial and boundary conditions where observed data are not available. The analytical solution can be well recovered if the boundary and initial conditions are properly handled. Next, we discuss the preprocessing procedure for the noisy bottom boundary data, and find that preprocessing is necessary for NLFFF extrapolations when we use the observed photospheric magnetic field as bottom boundaries. Finally, we apply the NLFFF model to a solar area where four active regions interacting with each other. An M8.7 flare occurred in one active region. NLFFF modeling in spherical geometry simultaneously constructs the small and large scale magnetic field configurations better than the PFSS model does.

scholarly journals Simulating the Coronal Evolution of Bipolar Active Regions to Investigate the Formation of Flux Ropes

Solar Physics ◽  
2021 ◽  
Vol 296 (1) ◽  
Author(s):  
S. L. Yardley ◽  
D. H. Mackay ◽  
L. M. Green
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Initial Conditions ◽  
Free Field ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Solar Dynamics Observatory ◽  
Horizontal Magnetic Field ◽  
Nonlinear Force ◽  
Force Free Field

AbstractThe coronal magnetic field evolution of 20 bipolar active regions (ARs) is simulated from their emergence to decay using the time-dependent nonlinear force-free field method of Mackay, Green, and van Ballegooijen (Astrophys. J. 729, 97, 2011). A time sequence of cleaned photospheric line-of-sight magnetograms, which covers the entire evolution of each AR, is used to drive the simulation. A comparison of the simulated coronal magnetic field with the 171 and 193 Å observations obtained by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), is made for each AR by manual inspection. The results show that it is possible to reproduce the evolution of the main coronal features such as small- and large-scale coronal loops, filaments and sheared structures for 80% of the ARs. Varying the boundary and initial conditions, along with the addition of physical effects such as Ohmic diffusion, hyperdiffusion and a horizontal magnetic field injection at the photosphere, improves the match between the observations and simulated coronal evolution by 20%. The simulations were able to reproduce the build-up to eruption for 50% of the observed eruptions associated with the ARs. The mean unsigned time difference between the eruptions occurring in the observations compared to the time of eruption onset in the simulations was found to be ≈5 hrs. The simulations were particularly successful in capturing the build-up to eruption for all four eruptions that originated from the internal polarity inversion line of the ARs. The technique was less successful in reproducing the onset of eruptions that originated from the periphery of ARs and large-scale coronal structures. For these cases global, rather than local, nonlinear force-free field models must be used. While the technique has shown some success, eruptions that occur in quick succession are difficult to reproduce by this method and future iterations of the model need to address this.

scholarly journals Testing magnetohydrostatic extrapolation with radiative MHD simulation of a solar flare

2019 ◽  
Vol 631 ◽  
pp. A162 ◽  
Author(s):  
X. Zhu ◽  
T. Wiegelmann
Keyword(s):  
Magnetic Field ◽  
Solar Flare ◽  
Initial Conditions ◽  
Free Field ◽  
Optimization Method ◽  
Field Vector ◽  
Plasma Pressure ◽  
Nonlinear Force ◽  
The Magnetic Field ◽  
Force Free Field

Context. On the sun, the magnetic field vector is measured routinely solely in the photosphere. By using these photospheric measurements as a boundary condition, we developed magnetohydrostatic (MHS) extrapolation to model the solar atmosphere. The model makes assumptions about the relative importance of magnetic and non-magnetic forces. While the solar corona is force-free, this is not the case with regard to the photosphere and chromosphere. Aims. The model has previously been tested with an exact equilibria. Here we present a more challenging and more realistic test of our model with the radiative magnetohydrodynamic simulation of a solar flare. Methods. By using the optimization method, the MHS model computes the magnetic field, plasma pressure and density self-consistently. The nonlinear force-free field (NLFFF) and gravity-stratified atmosphere along the field line are assumed as the initial conditions for optimization. Results. Compared with the NLFFF, the MHS model provides an improved magnetic field not only in magnitude and direction, but also in magnetic connectivity. In addition, the MHS model is capable of recovering the main structure of plasma in the photosphere and chromosphere.

scholarly journals Nonlinear force-free modeling of magnetic fields in flare-productive active regions

2015 ◽  
Vol 11 (S320) ◽  
pp. 167-174
Author(s):  
M. S. Wheatland ◽  
S. A. Gilchrist
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Boundary Data ◽  
Numerical Solutions ◽  
Free Field ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Nonlinear Force ◽  
The Magnetic Field ◽  
Force Free Field

AbstractWe review nonlinear force-free field (NLFFF) modeling of magnetic fields in active regions. The NLFFF model (in which the electric current density is parallel to the magnetic field) is often adopted to describe the coronal magnetic field, and numerical solutions to the model are constructed based on photospheric vector magnetogram boundary data. Comparative tests of NLFFF codes on sets of boundary data have revealed significant problems, in particular associated with the inconsistency of the model and the data. Nevertheless NLFFF modeling is often applied, in particular to flare-productive active regions. We examine the results, and discuss their reliability.

Studying Magnetic Field Variations Accompanying the 2011 June 7 Eruptive Event, by Using Nonlinear Force-Free Field Modeling

Solar Physics ◽  
2020 ◽  
Vol 295 (4) ◽  
Author(s):  
Y. I. Egorov ◽  
V. G. Fainshtein ◽  
I. I. Myshyakov ◽  
S. A. Anfinogentov ◽  
G. V. Rudenko
Keyword(s):  
Magnetic Field ◽  
Free Field ◽  
Eruptive Event ◽  
Field Modeling ◽  
Nonlinear Force ◽  
Magnetic Field Variations ◽  
Force Free Field

scholarly journals Chromospheric Magnetic Field: A Comparison of He i 10830 Å Observations with Nonlinear Force-free Field Extrapolation

2020 ◽  
Vol 898 (1) ◽  
pp. 32 ◽  
Author(s):  
Yusuke Kawabata ◽  
Andrés Asensio Ramos ◽  
Satoshi Inoue ◽  
Toshifumi Shimizu
Keyword(s):  
Magnetic Field ◽  
Free Field ◽  
Nonlinear Force ◽  
Force Free Field

scholarly journals Computational Modeling of Solar Magnetic Fields

1993 ◽  
Vol 141 ◽  
pp. 91-97
Author(s):  
Takashi Sakurai
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Free Field ◽  
Surface Model ◽  
Source Surface ◽  
Solar Magnetic Fields ◽  
Modeling Techniques ◽  
Proper Definition ◽  
Definition Of ◽  
Force Free Field

AbstractModeling techniques for solar magnetic fields are discussed. As an extension of the source surface model for large scale solar magnetic fields, a method based on the Green’s function approach to the Laplace equation is proposed. In the force-free field modeling, a proper definition of the boundary condition is an important but still unresolved problem. A condition based on the continuity of the Maxwell stress is newly proposed.

scholarly journals Interplanetary conditions: lessons from this minimum

2011 ◽  
Vol 7 (S286) ◽  
pp. 168-178 ◽  
Author(s):  
J. Luhmann ◽  
C. O. Lee ◽  
P. Riley ◽  
L. K. Jian ◽  
C. T. Russell ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Minimum ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Field Source ◽  
Mass Fluxes ◽  
Solar Wind Structure ◽  
Cycle 24

AbstractInterplanetary conditions during the Cycle 23-24 minimum have attracted attention because they are noticeably different than those during other minima of the space age, exhibiting more solar wind stream interaction structures in addition to reduced mass fluxes and low magnetic field strengths. In this study we consider the differences in the solar wind source regions by applying Potential Field Source Surface models of the coronal magnetic field. In particular, we consider the large scale coronal field geometry that organizes the open field region locations and sizes, and the appearance of the helmet streamer structure that is another determiner of solar wind properties. The recent cycle minimum had an extraordinarily long entry phase (the decline of Cycle 23) that made it difficult to identify when the actual miminum arrived. In particular, the late 23rd cycle was characterized by diminishing photospheric fields and complex coronal structures that took several extra years to simplify to its traditional dipolar solar minimum state. The nearly dipolar phase, when it arrived, had a duration somewhat shorter than those of the previous cycles. The fact that the corona maintained an appearance more like a solar maximum corona through most of the quiet transitional phase between Cycles 23 and 24 gave the impression of a much more complicated solar minimum solar wind structure in spite of the weaknesses of the mass flux and interplanetary field. The extent to which the Cycle 23-24 transition will affect Cycle 24, and/or represents what happens during weak cycles in general, remains to be seen.

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