Reconstruction of an evolving magnetic flux rope in the solar wind: Decomposing spatial and temporal variations from single‐spacecraft data

Abstract

AbstractWe present a novel single‐spacecraft method for decomposing spatial and temporal variations of physical quantities at points along the path of a spacecraft in space‐time. The method is designed for use in the reconstruction of evolving two‐dimensional, approximately magnetohydrostatic structures in a space plasma. It is an extension of the one developed by Sonnerup and Hasegawa (2010) and Hasegawa et al. (2010), in which it was assumed that variations in the time series of data, recorded as the structures move past the spacecraft, are all due to spatial effects. In reality, some of the observed variations are usually caused by temporal evolution of the structure during the time it moves past the observing spacecraft; the information in the data about the spatial structure is aliased by temporal effects. The purpose here is to remove this time aliasing from the reconstructed maps of field and plasma properties. Benchmark tests are performed by use of synthetic data taken by a virtual spacecraft as it traverses, at a constant velocity, a magnetic flux rope growing sufficiently slowly (relative to the Alfvén speed) in a two‐dimensional magnetohydrodynamic simulation of magnetic reconnection. These tests show that the new method can better recover the space‐time behavior of the flux rope than does the original version, in which time‐aliasing effects had not been removed. An application of the new method to a solar wind flux rope, observed by the ACE spacecraft, suggests that the cross‐sectional shape of the core part of the flux rope was varying.