Nonlinear force-free models for the solar corona

Régnier, Stéphane; Priest, E. R.

doi:10.1051/0004-6361:20077318

Cited by 51 publications

(48 citation statements)

References 45 publications

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“…The non-potential energy is concentrated near the base of the coronal volume, especially for AR 8210, as one would expect. It is noteworthy that (Régnier and Priest 2007) find non-potential excess energies considerably less than 10 32 erg for each region, even though AR 8210 did produce an X-class flare. In general it appears that the coronal field extrapolations do not capture the flare energy sources well at the present time ).…”

Section: Staticmentioning

confidence: 85%

“…4.2.2 and note that careful analysis with vector magnetogram data may in fact show no sign of relaxation to an LFFF state (Bleybel et al 2002). Figure 22 shows representative examples of NLFFF field extrapolation from the photosphere into the corona for two particular active regions (Régnier and Priest 2007). For the volume modeled in each region, the plots show the mean energy density vs height, and the fraction of "non-potential energy density" as an upper limit to what could be released by a flare.…”

Section: Staticmentioning

confidence: 99%

“…The observed variations thus Fig. 22 The results of potential (lower curves) and non-linear force-free (upper curves) extrapolations from photospheric vector field measurements from Régnier and Priest (2007) for two solar active regions (NOAA AR 8151 and 8210, respectively). The inset plots show the variation of non-potential energy density with height Fig.…”

Section: Dynamicmentioning

confidence: 99%

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Global Properties of Solar Flares

2011

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This article broadly reviews our knowledge of solar flares. There is a particular focus on their global properties, as opposed to the microphysics such as that needed for magnetic reconnection or particle acceleration as such. Indeed solar flares will always remain in the domain of remote sensing, so we cannot observe the microscales directly and must understand the basic physics entirely via the global properties plus theoretical inference. The global observables include the general energetics-radiation in flares and mass loss in coronal mass ejections (CMEs)-and the formation of different kinds of ejection and global wave disturbance: the type II radio-burst exciter, the Moreton wave, the EIT "wave", and the "sunquake" acoustic waves in the solar interior. Flare radiation and CME kinetic energy can have comparable magnitudes, of order 10 32 erg each for an X-class event, with the bulk of the radiant energy in the visible-UV continuum. We argue that the impulsive phase of the flare dominates the energetics of all of these manifestations, and also point out that energy and momentum in this phase largely reside in the electromagnetic field, not in the observable plasma.

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Section: Staticmentioning

confidence: 85%

Section: Staticmentioning

confidence: 99%

Section: Dynamicmentioning

confidence: 99%

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Global Properties of Solar Flares

2011

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“…This is important because the overlying coronal arcade plays a key role in the equilibrium and stability of the flux rope. For example, Régnier and Priest (2007) construct NLFFF models by "extrapolating" observed photospheric vector fields into the corona (also see Régnier et al, 2002;Régnier and Amari, 2004;Régnier and Canfield, 2006;Canou et al, 2009). They consider two active regions: one a decaying active region with strong currents (AR 8151), the other a newly emerged active region with weak currents (AR 8210).…”

Section: Non-linear Force-free Field Modelsmentioning

confidence: 99%

Physics of Solar Prominences: II—Magnetic Structure and Dynamics

et al. 2010

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Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.

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“…Even if the current density can be estimated on the photosphere, it is not intuitively clear how the change in the current density distribution affects a coronal magnetic configuration. Régnier & Priest (2007b) studied these modifications in terms of the geometry of field lines, the storage of magnetic energy, and the amount of magnetic helicity. Figure 5 shows iso-surface plots of current density above the volume of the active region.…”

Section: Resultsmentioning

confidence: 99%

Nonlinear force-free field extrapolation in spherical geometry: improved boundary data treatment applied to a SOLIS/VSM vector magnetogram

Tadesse

Wiegelmann

Inhester

et al. 2011

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Context. Understanding the 3D structure of coronal magnetic field is important to understanding: the onset of flares and coronal mass ejections, and the stability of active regions, and to monitoring the magnetic helicity and free magnetic energy and other phenomena in the solar atmosphere. Routine measurements of the solar magnetic field are mainly carried out in the photosphere. Therefore, one has to infer the field strength in the upper layers of the solar atmosphere from the measured photospheric field based on the assumption that the corona is force-free. Meanwhile, those measured data are inconsistent with the above force-free assumption. Therefore, one has to apply some transformations to these data before nonlinear force-free extrapolation codes can be applied. Aims. Extrapolation codes in Cartesian geometry for modelling the magnetic field in the corona do not take the curvature of the Sun's surface into account and can only be applied to relatively small areas, e.g., a single active region. Here we apply a method for nonlinear force-free coronal magnetic field modelling and preprocessing of photospheric vector magnetograms in spherical geometry using the optimization procedure. Methods. We solve the nonlinear force-free field equations by minimizing a functional in spherical coordinates over a restricted area of the Sun. We extend the functional by an additional term, which allows us to incorporate measurement errors and treat regions lacking observational data. We use vector magnetograph data from the Synoptic Optical Long-term Investigations of the Sun survey (SOLIS) to model the coronal magnetic field. We study two neighbouring magnetically connected active regions observed on May 15 2009. Results. For vector magnetograms with variable measurement precision and randomly scattered data gaps (e.g., SOLIS/VSM), the new code yields field models that satisfy the solenoidal and force-free condition significantly better as it allows deviations between the extrapolated boundary field and observed boundary data within the measurement errors. Data gaps are assigned an infinite error. We extend this new scheme to spherical geometry and apply it for the first time to real data.

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Nonlinear force-free models for the solar corona

Cited by 51 publications

References 45 publications

Global Properties of Solar Flares

Global Properties of Solar Flares

Physics of Solar Prominences: II—Magnetic Structure and Dynamics

Nonlinear force-free field extrapolation in spherical geometry: improved boundary data treatment applied to a SOLIS/VSM vector magnetogram

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