Method for inferring the axis orientation of cylindrical magnetic flux rope based on single‐point measurement

Abstract

[1] We develop a new simple method for inferring the orientation of a magnetic flux rope, which is assumed to be a time-independent cylindrically symmetric structure via the direct single-point analysis of magnetic field structure. The model tests demonstrate that, for the cylindrical flux rope regardless of whether it is force-free or not, the method can consistently yield the axis orientation of the flux rope with higher accuracy and stability than the minimum variance analysis of the magnetic field and the Grad-Shafranov reconstruction technique. Moreover, the radial distance to the axis center and the current density can also be estimated consistently. Application to two actual flux transfer events observed by the four satellites of the Cluster mission demonstrates that the method is more appropriate to be used for the inner part of flux rope, which might be closer to the cylindrical structure, showing good agreement with the results obtained from the optimal Grad-Shafranov reconstruction and the least squares technique of Faraday's law, but fails to produce such agreement for the outer satellite that grazes the flux rope. Therefore, the method must be used with caution.

On the origins of magnetic flux ropes in near‐Mars magnetotail current sheets

“…The other is that some previous studies pointed out that the MVA results might be unreliable in determining the flux rope axial orientation in some cases, depending on the crossing geometry of the spacecraft relative to the flux rope structure [e.g., Xiao et al, 2004;Rong et al, 2013]. However, in this study, we have visually inspected each individual flux rope events to confirm that their axial orientations (core field directions) adopted from the MVA results have the unimodal peak signature.…”

Automated force‐free flux rope identification

“…To test the efficacy of the method, it has been applied to the same data set as that previously investigated by DiBraccio et al [2015]. During 30 MESSENGER magnetotail current sheet encounters, between 2011and 2013, DiBraccio et al [2015 identified a total of 49 flux ropes. The three-step process independently reidentifies eight of these.…”

Formation processes of flux ropes downstream from Martian crustal magnetic fields inferred from Grad‐Shafranov reconstruction

“…Since the flux rope axis is identical with the invariant (GSR z ) axis, it is also determined so that magnetic field rotation perpendicular to the estimated rope axis obeys the right‐handed screw rule. To assess the validity of the derived flux rope orientation, we compare our GSR result with the one‐dimensional cylindrical geometric structure analysis method recently presented by Rong et al []. This method utilizes the single‐point magnetic field data and infers a flux rope's axial orientation with high accuracy and stability [ Rong et al , ].…”