Analysis of the heliospheric current sheet’s local structure based on a magnetic model

Abstract

Context. An approach to the problem of estimating several physical properties of the heliospheric current sheet (HCS) local structure from a single spacecraft observation point of view was published in 2003. This method, HYperbolic TAngent ROtation (HYTARO), is based on the following two main assumptions: (a) that the HCS is locally flat, and (b) that its magnetic topology is described by a modified Harris field. Aims. A revision of HYTARO by including the spacecraft’s trajectory and developing a more precise procedure able to reduce the number of the required fit parameters is presented in this paper. Methods. This magnetic topology is proposed for the HCS’s local field at 1 AU, and it was applied as a fit function to a collection of 40 HCS crossings detected by the WIND spacecraft during the solar minimum. The estimated HCS local parameters (i.e., orientation and width) are consistent with previous works, which used the minimum variance analysis or the coplanarity variance analysis, and this is inferred from HYTARO results. One of the points of discussion about HYTARO was determining if it was necessary to apply two or three rotations to characterize the field’s relative orientation with respect to the current sheet (CS) plane. As principal component analysis (PCA) is a method to decompose a set of data into no correlated components by identifying eigenvalues and eigenvectors, it is feasible to analyze the possibility of reducing the dimensionality of the problem. Results. HYTARO gives a qualitative description of the observed magnetic field during an HCS crossing. The number of free parameters from the original HYTARO method has been reduced including the relative spacecraft trajectory through the CS and adding a background field related to each Cartesian component. Further, PCA has been implemented to justify applying two rotations with the HYTARO model. The dimensionality is another way to explore the number of rotations needed to relate the field in the local system with the field in GSE coordinates.