[P-EM18] Heliosphere and Interplanetary Space

[PEM18-01] Problems in determining structures of interplanetary magnetic flux ropes

*Katsuhide Marubashi¹, Yuki Kubo¹, Nobuhiko Nishimura², Munetoshi Tokumaru², Nada Al-Haddad³ (1.National Institute of Information and Communications Technology , 2.ISEE, Nagoya University, 3.IACS, Catholic University of America)

Keywords:interplanetary flux rope, force-free model, Grad-Shafranov equation

The interplanetary magnetic flux ropes (IFRs) are ejected from the Sun to interplanetary space in association with the coronal mass ejections (CMEs). Their magnetic structure is an important research subject which provides information on the mechanism of CMEs. On the other hand, The IFRs often cause strong geomagnetic storms because of intense southward magnetic fields carried from the solar atmosphere. Thus, the IFRs have long been studied since they were discovered more than 30 years ago. It is the first step for such studies to determine the 3-D geometries and internal magnetic field structures of IFRs. We need to assume a physical model of the IFR and compare the model structure with observations. There are 2 representative analysis methods which are currently used along the line. They are: (1) a fitting method to models of force-free magnetic field configurations, and (2) a reconstruction method of magnetic field structures based on the Grad-Shafranov (GS) equation. Recently, Al-Haddad et al. (Solar Phys. 2018) examined the mutual agreement between the results from the two methods for 13 well-determined IFRs carefully selected. They found that the agreement is relatively good in only 6 cases, and thus concluded that the compatibility of different models with specific IFR structures must be taken into account.

The present study is an extension of the work by Al-Haddad et al. In the GS method, 2-D structure (essentially a cylindrical structure) is assumed, and the axis orientation is determined so that the symmetry condition is satisfied between inbound and outbound crossings of the IFR. If the IFR fields satisfy the force-free condition, the internal structures obtained by the 2 methods agree with each other. Actually, however, the GS method includes the effect of plasma pressure while the force-free model neglects the plasma pressure. This can cause the discrepancy between the two. With this idea in mind, we started to examine how the axis orientations deviate from each other. However, we encounter an unexpected problem, that is, it is not easy to point start and end times of an IFR from the observed data. Especially in the GS method, the selection of the IFR interval is strongly affected by the symmetry condition. In this presentation we show results of our trial to determine the axis orientation for many possible IFR intervals.