The free energies of partially open coronal magnetic fields

Low, B. C.; Smith, D. F.

doi:10.1086/172758

Cited by 95 publications

(72 citation statements)

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“…CMEs may form into flux ropes as they develop [e.g., Low and Smith, 1993;Chen, 1996] and/or as they leave the Sun [Gosling, 1990]. Roughly 30% of CMEs identified in the solar wind show the large-scale field rotations characteristic of flux ropes [Gosling, 1990].…”

Section: Introductionmentioning

confidence: 99%

A test of real‐time prediction of magnetic cloud topology and geomagnetic storm occurrence from solar signatures

McAllister¹,

Martin²,

Crooker³

et al. 2001

J. Geophys. Res.

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Abstract.On the basis of the location, orientation, and surrounding magnetic field configuration of an erupting filament observed on September 27, 1997, an Earth-encounter with a magnetic cloud having specific topological properties and an ensuing geomagnetic storm were predicted for September 30, assuming an average Sun-Earth transit time. A subsequent comparison with solar wind and geomagnetic data surrounding September 30 yielded a mixed level of success. Although a geomagnetic storm occurred on October 1, ironically, the strong southward magnetic field responsible for it was not encountered at the leading edge of the cloud, as predicted, but rather in the preceding sheath. In retrospect, the most likely sources of the southward field in the sheath were either a preceding CME or magnetic flux from high in the corona, not draped or turbulent flux from the ambient solar wind as is often supposed. With the aid of a flux rope model, we show that the elevation and polarity of the cloud axis and the chirality of the cloud were predicted correctly but that the trajectory of the spacecraft (and Earth) through what was deduced to be the leg of a flux rope loop precluded encounter with its leading southward field. The storm began with a sudden commencement near 0100 UT on October 1, corresponding to passage of a shock-like discontinuity, and the Dst storm index reached a minimum of-108 nT 14 hours later at 1500 UT. The leading edge of the cloud, however, coincident with the onset of counterstreaming electrons confirming its identification, was not encountered until 1700 UT. The disagreement between the predicted and actual arrival time reflects not only the lack of speed prediction capabilities but also the inability to predict whether encounter will be head-on with the apex of a flux rope loop or, as deduced in this case, passage through one of its legs.

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Section: Introductionmentioning

confidence: 99%

A test of real‐time prediction of magnetic cloud topology and geomagnetic storm occurrence from solar signatures

McAllister¹,

Martin²,

Crooker³

et al. 2001

J. Geophys. Res.

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“…Since these speeds are typically less than the gravitational escape speed of •600 km s -• at the photosphere, then both pressure and magnetic forces must dominate the gravitational force during the ejection of a CME (e.g., see reviews by Low [1993] and Low and Smith [1993]). …”

Section: Introductionmentioning

confidence: 99%

A comparison of ground‐based and spacecraft observations of coronal mass ejections from 1980–1989

Cyr¹,

Burkepile²,

Hundhausen³

et al. 1999

J. Geophys. Res.

162

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“…Although Aly's constraint is relevant only to force-free fields, the Aly limit as defined here is the energy threshold for any magnetic field to open up by its own energy. Figure 5b shows that the total magnetic energy of A smooth exceeds the Aly limit for a > 1:3r 0 , due principally to the presence of magnetic flux in r > r 0 not anchored to the inner boundary (Low & Smith 1993). Such unanchored flux generally requires plasma weight for confinement via nonzero Lorentz forces.…”

Section: Finite-width Prominence Sheetsmentioning

confidence: 95%

“…This virial equation remains valid if the hydromagnetic equilibrium contains magnetic tangential discontinuities in force balance with continuity of the total pressure across them (Low & Smith 1993). Thus, the magnetic energy in r > r 0 for our flux-rope solution may be written as 1 8…”

Section: Virial Theoremmentioning

confidence: 99%

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Quiescent Solar Prominences and Magnetic‐Energy Storage

Fong¹,

Low²,

Fan³

2002

ApJ

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Analytical solutions are presented to describe the hydromagnetic support of quiescent solar prominences treated as cold plasma sheets in the characteristic normal and inverse configurations. The solar corona is modeled to be axisymmetric outside a unit sphere, with the prominence sheet lying in the equatorial plane extending from the sphere out to a finite radial distance subject to an inverse-square Newtonian gravity. The relationship between prominence support and the global topology of the surrounding poloidal magnetic field is discussed, with a particular interest in the role of magnetic flux ropes in the support of inverse prominences. A novel solution is also studied describing a rope of purely azimuthal magnetic flux held in equilibrium by the weight of an internal distribution of cold mass and by an external poloidal magnetic field rigidly anchored to the base of the model corona. This solution illustrates the role that prominence weight may play in storing magnetic energy for driving coronal mass ejections.

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The free energies of partially open coronal magnetic fields

Cited by 95 publications

References 0 publications

A test of real‐time prediction of magnetic cloud topology and geomagnetic storm occurrence from solar signatures

A test of real‐time prediction of magnetic cloud topology and geomagnetic storm occurrence from solar signatures

A comparison of ground‐based and spacecraft observations of coronal mass ejections from 1980–1989

Quiescent Solar Prominences and Magnetic‐Energy Storage

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