Origin and structures of solar eruptions II: Magnetic modeling

Abstract

The topology and dynamics of the three-dimensional magnetic field in the solar atmosphere govern various solar eruptive phenomena and activities, such as flares, coronal mass ejections, and filaments/prominences. We have to observe and model the vector magnetic field to understand the structures and physical mechanisms of these solar activities. Vector magnetic fields on the photosphere are routinely observed via the polarized light, and inferred with the inversion of Stokes profiles. To analyze these vector magnetic fields, we need first to remove the 180 • ambiguity of the transverse components and correct the projection effect. Then, the vector magnetic field can be served as the boundary conditions for a force-free field modeling after a proper preprocessing. The photospheric velocity field can also be derived from a time sequence of vector magnetic fields. Three-dimensional magnetic field could be derived and studied with theoretical force-free field models, numerical nonlinear force-free field models, magnetohydrostatic models, and magnetohydrodynamic models. Magnetic energy can be computed with three-dimensional magnetic field models or a time series of vector magnetic field. The magnetic topology is analyzed by pinpointing the positions of magnetic null points, bald patches, and quasi-separatrix layers. As a well conserved physical quantity, magnetic helicity can be computed with various methods, such as the finite volume method, discrete flux tube method, and helicity flux integration method. This quantity serves as a promising parameter characterizing the activity level of solar active regions.

A Study of Pre-flare Solar Coronal Magnetic Fields: Magnetic Flux Ropes

“…For instance, X-ray and EUV sigmoid, filament, EUV hot channel, and coronal cavity are invoked as indirect observations of coronal MFRs (e.g., see a recent review paper by Cheng et al 2017). Using nonlinear force-free field (NLFFF) extrapolations from vector magnetograms, which is a basic tool for unraveling the 3D information of solar coronal magnetic field, MFRs were identified frequently (e.g., see another recent review by Guo et al 2017).…”

Probing the Production of Extreme-ultraviolet Late-phase Solar Flares Using the Model Enthalpy-based Thermal Evolution of Loops

“…Case studies showed that EUV late-phase flares occur in a multipolar magnetic field, which exhibits either a classic or asymmetric quadrupolar configuration Liu et al 2013a), or a parasitic polarity embedded in a large-scale bipolar magnetic field (Dai et al 2013;Sun et al 2013;Masson et al 2017). Such a magnetic configuration observationally facilitates the existence of two sets of loops that are distinct in length rather than loops with a continuous length distribution, as further confirmed by force-free coronal magnetic field extrapolations (Jiang et al 2013;Sun et al 2013;Li et al 2014a;Guo et al 2017;Masson et al 2017).…”

Magnetic structure of solar flare regions producing hard X-ray pulsations

“…We chose the data for the instants of time before the flares, within 2 − 31 minutes prior to the flare onset times according to the GOES data (see Table 1 in Paper-I). It is known that the magnetic field reconstructed in the NLFF approximation usually does not change significantly on a time scale of a few tens of minutes (e.g., Guo et al, 2008;Liu et al, 2016b;Guo et al, 2017). The selected regions have a rectangular shape in the helioprojective-cartesian (HPC) coordinates (Thompson, 2006).…”