Plasma Loops in the Solar Corona

Bray, R. J.; Cram, L. E.; Durrant, C. J.; Loughhead, R. E.

doi:10.1017/cbo9780511600111

Cited by 229 publications

(146 citation statements)

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“…2 showing an overlay of magnetogram and emission. This is consistent with the long-known observation fact that the footpoints of coronal loops are not in the umbra at the higher field strengths, but in the periphery, the penumbra (Bray et al 1991). Even though the flux emergence simulation does not contain a proper penumbra (Cheung et al 2010) it is clear that the loops are rooted in a region where convection can do considerable work to the magnetic field in the photosphere (see Sect.…”

Section: Hrsupporting

confidence: 88%

A model for the formation of the active region corona driven by magnetic flux emergence

Chen

Peter

Bingert

et al. 2014

A&A

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Aims. We present the first model that couples the formation of the corona of a solar active region to a model of the emergence of a sunspot pair. This allows us to study when, where, and why active region loops form, and how they evolve. Methods. We use a 3D radiation magnetohydrodynamics (MHD) simulation of the emergence of an active region through the upper convection zone and the photosphere as a lower boundary for a 3D MHD coronal model. The coronal model accounts for the braiding of the magnetic fieldlines, which induces currents in the corona to heat up the plasma. We synthesize the coronal emission for a direct comparison to observations. Starting with a basically field-free atmosphere we follow the filling of the corona with magnetic field and plasma. Results. Numerous individually identifiable hot coronal loops form, and reach temperatures well above 1 MK with densities comparable to observations. The footpoints of these loops are found where small patches of magnetic flux concentrations move into the sunspots. The loop formation is triggered by an increase in upward-directed Poynting flux at their footpoints in the photosphere. In the synthesized extreme ultraviolet (EUV) emission these loops develop within a few minutes. The first EUV loop appears as a thin tube, then rises and expands significantly in the horizontal direction. Later, the spatially inhomogeneous heat input leads to a fragmented system of multiple loops or strands in a growing envelope.

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Section: Hrsupporting

confidence: 88%

A model for the formation of the active region corona driven by magnetic flux emergence

Chen

Peter

Bingert

et al. 2014

A&A

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“…whatever the temperature, the selection must actually take place only from lower temperature gases, in the 2.5-5 MK range. These selection temperatures are comparable to, but distinctly higher than, the common quiescent active region temperatures of -2-3.5 MK (Webb 1981;Bray et al 1991;Saba & Strong 1991a, b). Solar Maximum Mission (SMM) observations suggest that elevated temperatures may be found commonly in active regions for up to an hour after a flare.…”

Section: Temperatures Of the Gases From Which The Heavy Ions Are Selesupporting

confidence: 49%

Energetic-Particle Abundances in Impulsive Solar Flare Events

Reames

Meyer²,

Rosenvinge³

1994

International Astronomical Union Colloquium

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We report on the abundances of energetic particles from impulsive solar flares, including those from a survey of 228 3 He-rich events, with 3 He/ 4 He > 0.1, observed by the ISEE 3 spacecraft from 1978 August through 1991 April. The rate of occurrence of these events corresponds to ~1000 events yr -1 on the solar disk at solar maximum. Thus the resonant plasma processes that enhance 3 He and heavy elements are a common occurrence in impulsive solar flares. To supply the observed fluence of 3 He in large events, the acceleration must be highly efficient and the source region must be relatively deep in the atmosphere at a density of more than 10 10 atoms cm" 3 . 3 He/ 4 He may decrease in very large impulsive events because of depletion of 3 He in the source region.The event-to-event variations in 3 He/ 4 He, H/ 4 He, e/p, and Fe/C are uncorrected in our event sample. Abundances of the elements show a pattern in which, relative to coronal composition, 4 He, C, N, and O have normal abundance ratios, while Ne, Mg, and Si are enhanced by a factor ~2.5 and Fe by a factor ~7 . This pattern suggests that elements are accelerated from a region of the corona with an electron temperature of ~3 -5 MK, where elements in the first group are fully ionized (Q/A = 0.5), those in the second group have two orbital electrons (Q/A ~ 0.43), and Fe has Q/A ~ 0.28. Ions with the same gyrofrequency absorb waves of that frequency and are similarly accelerated and enhanced. Further stripping may occur after acceleration as the ions begin to interact with the streaming electrons that generated the plasma waves.

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“…One-dimensional models have been used to investigate coronal loops in the closedÐeld region (static models such as Rosner, Tucker, & Vaiana 1978 ;Craig, McClymont, & Underwood 1978 ;Hood & Priest 1979 ;Vesecky, Antiochos, & Underwood 1979 ;Serio et al 1981 ; as well as numerical hydrodynamic simulations, see Klimchuk, Antiochos, & Mariska 1987 ;Mok, Schnack, & Van Hoven 1991 ; see also Bray, Cram, & Durrant 1991 for a review) and the solar wind outÑow in coronal holes (Hammer 1982a(Hammer , 1982bWithbroe 1988 ;Hansteen & Leer 1995 ;Habbal et al 1995 ;Hansteen, Leer, & Holzer 1997). One-dimensional models have the advantage that it is relatively easy to include complicated dynamic and thermodynamic e †ects such as thermal conduction, and computations are not usually very CPU intensive, but they have obvious geometric limitations.…”

Section: Introductionmentioning

confidence: 99%

Including the Transition Region in Models of the Large‐Scale Solar Corona

Lionello

Linker

Mikić

2001

ApJ

118

103

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In traditional multidimensional models of the solar corona, the boundary of the calculation closest to the solar surface is placed well into the corona (at temperatures of 1È2 ] 106 K). We describe a largescale MHD model that includes the transition region in the calculation. In this model, we simulate the solar atmosphere from the top of the chromosphere (at 20,000 K), through the transition region, into the corona, and extending out into the inner heliosphere. Our model includes parallel thermal conduction, coronal heating, and radiation losses in the energy equation. For simplicity, we describe a twodimensional (axisymmetric) implementation of our model. This model enables us to study the large-scale structure of the transition region. In particular, we contrast the variation of the structure of the transition region underneath a closed magnetic arcade with that in an open-Ðeld region. We discuss how the inclusion of the transition region and upper chromosphere into the model modiÐes the time constants. We compare our results with a model in which the calculation is started near the top of the transition region (at 500,000 K) using a "" radiative energy balance ÏÏ condition, and we Ðnd that the two models agree well in open-Ðeld regions and for long loops. However, a model that includes the transition region is required to properly model short loops in closed-Ðeld regions.

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Plasma Loops in the Solar Corona

Cited by 229 publications

References 0 publications

A model for the formation of the active region corona driven by magnetic flux emergence

A model for the formation of the active region corona driven by magnetic flux emergence

Energetic-Particle Abundances in Impulsive Solar Flare Events

Including the Transition Region in Models of the Large‐Scale Solar Corona

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