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Examining the Magnetic Geometry of Magnetic Flux Ropes from the View of Single-point Analysis

Magnetic flux ropes, characterized as magnetic field lines that wrap and rotate around a central axis, are observed ubiquitously in the space-plasma environment. Accurately examining the physical parameters (e.g., axis orientation, helical handedness, current density, curvature radius, and size) of flux ropes is essential for studying their evolution and associated dynamics. The geometric parameters of flux ropes can be resolved by a cluster of at least four spacecraft with the separation scale much smaller than the flux ropes. However, most spacecraft missions are of single-point measurements, especially for the missions on other planets (e.g., Mars, Venus, Mercury), thus, the method for investigating the flux ropes based on single-point measurements becomes particularly important. A single-point method that infers the axis orientation of flux ropes was recently developed by Rong et al. Here, we apply this method to study two flux ropes observed by the Magnetospheric Multiscale Mission (MMS), one close to the force-free field and the other close to the non-force-free field, by comparing them with the multipoint analysis of MMS. Our study demonstrates that, apart from axis orientation, the method of Rong et al. can reasonably infer the current density, curvature radius of magnetic field, and the transverse size of flux ropes. We discussed the main error sources of calculated parameters, and suggest that it is worthwhile to widely apply the method by Rong et al. to single-point spacecraft missions for the purpose of examining the geometry and dynamics of flux ropes.