Automated force‐free flux rope identification

Smith, A. W.; Slavin, J. A.; Jackman, C. M.; Fear, R. C.; Poh, Gangkai; DiBraccio, G. A.; Jasinski, Jamie M.; Trenchi, Lorenzo

doi:10.1002/2016ja022994

Cited by 17 publications

(32 citation statements)

References 72 publications

(112 reference statements)

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“…For a full, comprehensive description of the flux rope identification method the reader is directed to Smith et al []. In summary, the following steps are used to identify flux rope encounters: Baseline crossing and peak detection: Significant deflections of the north‐south component of the magnetic field are located.…”

Section: Methodsmentioning

confidence: 99%

Flux ropes in the Hermean magnetotail: Distribution, properties, and formation

et al. 2017

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An automated method was applied to identify magnetotail flux rope encounters in MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) magnetometer data. The method identified significant deflections of the north‐south component of the magnetic field coincident with enhancements in the total field or dawn‐dusk component. Two hundred forty‐eight flux ropes are identified that possess well‐defined minimum variance analysis (MVA) coordinate systems, with clear rotations of the field. Approximately 30% can be well approximated by the cylindrically symmetric, linearly force‐free model. Flux ropes are most common moving planetward, in the postmidnight sector. Observations are intermittent, with the majority (61%) of plasma sheet passages yielding no flux ropes; however, the peak rate of flux ropes during a reconnection episode is ∼5 min−1. Overall, the peak postmidnight rate is ∼0.25 min−1. Only 25% of flux ropes are observed in isolation. The radius of flux ropes is comparable to the ion inertial length within Mercury's magnetotail plasma sheet. No clear statistical separation is observed between tailward and planetward moving flux ropes, suggesting the near‐Mercury neutral line (NMNL) is highly variable. Flux ropes are more likely to be observed if the preceding lobe field is enhanced over background levels. A very weak correlation is observed between the flux rope core field and the preceding lobe field orientation; a stronger relationship is found with the orientation of the field within the plasma sheet. The core field strength measured is ∼6 times stronger than the local dawn‐dusk plasma sheet magnetic field.

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Section: Methodsmentioning

confidence: 99%

Flux ropes in the Hermean magnetotail: Distribution, properties, and formation

et al. 2017

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“…where σ B Z is the local standard deviation of the B Z component and

r_{Min}^{'}

is the impact parameter of the flux rope encounter. Several other criteria were also placed upon the signature; for full details the interested reader is directed to Smith, Slavin, Jackman, Fear, et al (). The criteria based on the quality of model fit and results of the minimum variance analysis have not been included, they would not reject the model field signatures generated by the force‐free model.…”

Section: Evaluating Selection Biasmentioning

confidence: 99%

“…The criteria based on the quality of model fit and results of the minimum variance analysis have not been included, they would not reject the model field signatures generated by the force‐free model. In addition, Smith, Slavin, Jackman, Fear, et al () employed a wavelet transform in order to locate peaks in the axial and total field; this has also not been recreated by the method. In total, Smith, Slavin, Jackman, Poh, et al () located 248 flux ropes, of which 74 were found to be well fitted by the force‐free model.…”

Section: Evaluating Selection Biasmentioning

confidence: 99%

“…A commonly used criterion in magnetotail surveys is a fixed lower limit on the magnitude of the field deflection required (i.e., in the north‐south field component; e.g., Ieda et al, ; Moldwin & Hughes, ; Sun et al, ). More recently, in an attempt to identify smaller scale events, criteria have been developed that require deviation above the level of background fluctuations of the field, particularly at Jupiter (Vogt et al, ), Saturn (Jackman et al, ; Smith et al, ), and Mercury (Smith, Slavin, Jackman, Fear, et al, ). Criteria can also be placed upon the enhancements observed in the axial direction and the total field (e.g., Sun et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…Assuming that the flux ropes traveled at approximately the average Alfvén velocity (465 km/s; DiBraccio et al, ), and correcting for the trajectory of the spacecraft, the average radius was found to be 345 km; much smaller than the previous observations. More recently, Smith, Slavin, Jackman, Poh, et al () identified 248 flux ropes using an automated procedure (Smith, Slavin, Jackman, Fear, et al, ), and recorded an average duration of 0.83 s. Approximately 30% (74) of the flux ropes were found to be well modeled by the cylindrically symmetric force‐free model. This allowed the approximate spacecraft trajectory through the structure to be modeled and the duration to be corrected for the relative impact parameter.…”

Section: Introductionmentioning

confidence: 99%

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Evaluating Single Spacecraft Observations of Planetary Magnetotails With Simple Monte Carlo Simulations: 2. Magnetic Flux Rope Signature Selection Effects

et al. 2018

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A Monte Carlo method of investigating the effects of placing selection criteria on the magnetic signature of in situ encounters with flux ropes is presented. The technique is applied to two recent flux rope surveys of MESSENGER data within the Hermean magnetotail. It is found that the different criteria placed upon the signatures will preferentially identify slightly different subsets of the underlying population. Quantifying the selection biases first allows the distributions of flux rope parameters to be corrected, allowing a more accurate estimation of the intrinsic distributions. This is shown with regard to the distribution of flux rope radii observed. When accounting for the selection criteria, the mean radius of Hermean magnetotail quasi‐force‐free flux ropes is found to be 58 km. Second, it is possible to weight the known identifications in order to determine a rate of recurrence that accounts for the presence of the structures that will not be identified. In the case of the Hermean magnetotail, the average rate of quasi‐force‐free flux ropes is found to 0.12 min −1 when selection effects are accounted for (up from 0.05 min −1 previously inferred from observations).

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The Plasma Sheet as Natural Symmetry Plane for Dipolarization Fronts in the Earth's Magnetotail

Frühauff

Glassmeier

2017

JGR Space Physics

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In this work, observations of multispacecraft mission Time History of Events and Macroscale Interactions during Substorms are used for statistical investigation of dipolarization fronts in the near‐Earth plasma sheet of the magnetotail. Using very stringent criteria, 460 events are detected in almost 10 years of mission data. Minimum variance analysis is used to determine the normal directions of the phase fronts, providing evidence for the existence of a natural symmetry of these phenomena, given by the neutral sheet of the magnetotail. This finding enables the definition of a local coordinate system based on the Tsyganenko model, reflecting the intrinsic orientation of the neutral sheet and, therefore, the dipolarization fronts. In this way, the comparison of events with very different background conditions is improved. Through this study, the statistical results of Liu, Angelopoulos, Runov, et al. (2013) are both confirmed and extended. In a case study, the knowledge of this plane of symmetry helps to explain the concave curvature of dipolarization fronts in the XZ plane through phase propagation speeds of magnetoacoustic waves. A second case study is presented to determine the central current system of a passing dipolarization front through a constellation of three spacecraft. With this information, a statistical analysis of spacecraft observations above and below the neutral sheet is used to provide further evidence for the neutral sheet as the symmetry plane and the central current system. Furthermore, it is shown that the signatures of dipolarization fronts are under certain conditions closely related to that of flux ropes, indicating a possible relationship between these two transient phenomena.

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Automated force‐free flux rope identification

Cited by 17 publications

References 72 publications

Flux ropes in the Hermean magnetotail: Distribution, properties, and formation

Flux ropes in the Hermean magnetotail: Distribution, properties, and formation

Evaluating Single Spacecraft Observations of Planetary Magnetotails With Simple Monte Carlo Simulations: 2. Magnetic Flux Rope Signature Selection Effects

The Plasma Sheet as Natural Symmetry Plane for Dipolarization Fronts in the Earth's Magnetotail

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