Three-Year Global Survey of Coronal Null Points from Potential-Field-Source-Surface (PFSS) Modeling and Solar Dynamics Observatory (SDO) Observations

Freed, Michael; Longcope, D. W.; McKenzie, D. E.

doi:10.1007/s11207-014-0616-5

Cited by 22 publications

(27 citation statements)

References 47 publications

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“…In general, similar coronal loop formations have been attributed to there being a null point at the 'X' (e.g. [4,5]); however, it is possible that a separator may be present instead.…”

Section: Basic Elements Of the Three-dimensional Magnetic Skeletonmentioning

confidence: 88%

“…In about 31% of the cases, Freed et al [5] found that the AIA observations showed structures, such as X-type loop patterns, that could be interpreted as the configuration associated with a null point. However, since separators are field lines that generally extend from or to a null point, it is not unreasonable to imagine that in a proportion of the above cases, the coronal signature may reveal the location of a separator, rather than a null point.…”

Section: Basic Elements Of the Three-dimensional Magnetic Skeletonmentioning

confidence: 99%

“…[10,11]). Recently, the nulls that occur in PFSS models of the global coronal magnetic field [5,[12][13][14][15] have been counted.…”

Section: Three-dimensional Coronal Topologies: Global and Localmentioning

confidence: 99%

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Is magnetic topology important for heating the solar atmosphere?

Parnell

Stevenson

Threlfall

et al. 2015

Phil. Trans. R. Soc. A.

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Magnetic fields permeate the entire solar atmosphere weaving an extremely complex pattern on both local and global scales. In order to understand the nature of this tangled web of magnetic fields, its magnetic skeleton, which forms the boundaries between topologically distinct flux domains, may be determined. The magnetic skeleton consists of null points, separatrix surfaces, spines and separators. The skeleton is often used to clearly visualize key elements of the magnetic configuration, but parts of the skeleton are also locations where currents and waves may collect and dissipate. In this review, the nature of the magnetic skeleton on both global and local scales, over solar cycle time scales, is explained. The behaviour of wave pulses in the vicinity of both nulls and separators is discussed and so too is the formation of current layers and reconnection at the same features. Each of these processes leads to heating of the solar atmosphere, but collectively do they provide enough heat, spread over a wide enough area, to explain the energy losses throughout the solar atmosphere? Here, we consider this question for the three different solar regions: active regions, open-field regions and the quiet Sun. We find that the heating of active regions and open-field regions is highly unlikely to be due to reconnection or wave dissipation at topological features, but it is possible that these may play a role in the heating of the quiet Sun. In active regions, the absence of a complex topology may play an important role in allowing large energies to build up and then, subsequently, be explosively released in the form of a solar flare. Additionally, knowledge of the intricate boundaries of open-field regions (which the magnetic skeleton provides) could be very important in determining the main acceleration mechanism(s) of the solar wind.

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“…In general, similar coronal loop formations have been attributed to there being a null point at the 'X' (e.g. [4,5]); however, it is possible that a separator may be present instead.…”

Section: Basic Elements Of the Three-dimensional Magnetic Skeletonmentioning

confidence: 88%

Section: Basic Elements Of the Three-dimensional Magnetic Skeletonmentioning

confidence: 99%

See 1 more Smart Citation

Is magnetic topology important for heating the solar atmosphere?

Parnell

Stevenson

Threlfall

et al. 2015

Phil. Trans. R. Soc. A.

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“…Using this method, Eriksson et al (2015) performed a statistical study of magnetic nulls in the nightside magnetosphereand concluded that the number of spiral nulls prevailed over the number of radial ones. The global potential field extrapolations allowed us to locate a large number of magnetic nulls in the solar corona (Edwards & Parnell 2015;Freed et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Magnetic Null Points in Kinetic Simulations of Space Plasmas

Olshevsky

Deca

Divin

et al. 2016

ApJ

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We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic particle-in-cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind,and a relaxing turbulent configuration with multiple null points. Spiral nulls are more likely created in space plasmas: in all our simulations except lunar magnetic anomaly (LMA) and quadrupolar mini-magnetosphere the number of spiral nulls prevails over the number of radial nulls by a factor of 3-9. We show that often magnetic nulls do not indicate the regions of intensive energy dissipation. Energy dissipation events caused by topological bifurcations at radial nulls are rather rare and short-lived. The so-called X-lines formed by the radial nulls in the Harris current sheet and LMA simulations are rather stable and do not exhibit any energy dissipation. Energy dissipation is more powerful in the vicinity of spiral nulls enclosed by magnetic flux ropes with strong currents at their axes (their crosssections resemble 2D magnetic islands). These null lines reminiscent of Z-pinches efficiently dissipate magnetic energy due to secondary instabilities such as the two-stream or kinking instability, accompanied by changes in magnetic topology. Current enhancements accompanied by spiral nulls may signal magnetic energy conversion sites in the observational data.

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“…In contrast to Cook, Mackay, and Nandy (2009), they found that the most nulls occurred during solar minimum when extensive regions of mixed small-scale field are present on the solar surface. Freed, Longcope, and McKenzie (2015) also directly identified null points in PFSS extrapolations of the global corona. However, their PFSS extrapolations have a low resolution, with an l max = 30.…”

Section: Introductionmentioning

confidence: 88%

Null Point Distribution in Global Coronal Potential Field Extrapolations

Edwards

Parnell

2015

Sol Phys

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Magnetic null points are points in space where the magnetic field is zero. Thus, they can be important sites for magnetic reconnection by virtue of the fact that they are weak points in the magnetic field and also because they are associated with topological structures, such as separators, which lie on the boundary between four topologically distinct flux domains and therefore are also locations where reconnection occurs. The number and distribution of nulls in a magnetic field acts as a measure of the complexity of the field.In this paper, the numbers and distributions of null points in global potential field extrapolations from high-resolution synoptic magnetograms are examined. Extrapolations from MDI magnetograms are studied in depth and compared with those from high-resolution SOLIS and HMI.The fall off in the density of null points with height is found to follow a power law with a slope that differs depending on whether the data is from solar maximum or solar minimum. The distribution of null points with latitude also varies with the cycle as null points form predominantly over quiet-Sun regions and avoid active-region fields. The exception to this rule are the null points that form high in the solar atmosphere and these null points tend to form over large areas of strong flux in active regions.From case studies of the MDI, SOLIS and HMI data, it is found that the distribution of null points is very similar between data sets except, of course, there are far fewer nulls observed in the SOLIS data than the cases from MDI and HMI due to its lower resolution.

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Three-Year Global Survey of Coronal Null Points from Potential-Field-Source-Surface (PFSS) Modeling and Solar Dynamics Observatory (SDO) Observations

Cited by 22 publications

References 47 publications

Is magnetic topology important for heating the solar atmosphere?

Is magnetic topology important for heating the solar atmosphere?

Magnetic Null Points in Kinetic Simulations of Space Plasmas

Null Point Distribution in Global Coronal Potential Field Extrapolations

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