[P-EM16] Heliosphere and Interplanetary Space

[PEM16-P05] A new method for Grad-Shafranov reconstruction of interplanetary magnetic flux ropes

*Katsuhide Marubashi¹, Daikou Shiota¹, Yuki Kubo¹, Hasegawa Hiroshi², Munetoshi Tokumaru³ (1.National Institute of Information and Communications Technology, 2.Institute of Space and Astronautical Science, 3.Institute for Space-Earth Environmental Research, Nagoya University)

Keywords:interplanetary magnetic flux rope, solar wind magnetic field, magnetic field structure

The interplanetary magnetic flux ropes (IFRs) have long been studied because of their strong connection with coronal mass ejections (CMEs) and the geomagnetic storms. It is a key in such studies to determine the 3-D geometries and the internal magnetic field structure of IFRs. Two analysis methods have widely used for clarifying the structure of observed IFRs: (1) fitting of observed magnetic fields to force-free models (FF method), and (2) reconstruction of IFRs based on the Grad-Shafranov equation (GS method). One fundamental problem with the GS method is that it needs spatial distribution of magnetic field along a line which is used as a boundary condition for calculating the spatial structure of the IFR, while the observed fields obtained by spacecraft are combination of spatial and temporal variations. We developed a method to derive the spatial change along the spacecraft orbit for IFRs expanding in a self-similar fashion, for which it is valid to apply the GS method. We applied this newly-developed GS method to data sets prepared by theoretical force-free flux ropes which include self-similar expansion. Thus, we confirmed the applicability of the new GS method. At the same time, we examined how the expansion effects affect the performance of the traditional GS method. It can be said that the errors become larger as the expansion rate increases, and that the traditional method becomes no longer valid for large expansion rate. Finally, a more general theory was published about the GS method applicable to time-varying IFR model (Hasegawa et al., JGR 2014). We expect that by combining Hasegawa et al. method with the present method it may be able to distinguish the real spatial asymmetry and the virtual asymmetry due to expansion in the future.