[P-EM08] 宇宙天気・宇宙気候

[PEM08-16] Simulation study on the deformation of magnetic field in interplanetary CMEs

*森 美南¹、塩田 大幸²、草野 完也¹ (1.名古屋大学宇宙地球環境研究所、2.国立研究開発法人 情報通信研究機構)

キーワード：磁気流体シミュレーション、コロナ質量放出、太陽風

Coronal mass ejections (CMEs) are the largest eruption in the solar system. CMEs carry huge plasmas in the solar corona of 10^11 to 10^13 kg into interplanetary space at velocities of a few hundred - thousand km/s. CMEs can affect a variety of space weather conditions when they collide with the magnetosphere of the earth. In particular, the magnetic field of CMEs is a serious factor of space weather disturbance, because the southward component of the magnetic field in CMEs could cause the geomagnetic field storm. We developed a numerical simulation of CME propagation in the inner heliosphere using the magnetohydrodynamic (MHD) model, SUSANOO-CME (Shiota & Kataoka, 2016). In this model, the CME magnetic field is given by the distorted spheromak force-free field in which the orientation of the major axis and position of the spheromak is determined with free parameters. To make the simulation and its analysis simple, we assume that the major axis of the spheromak is on the equator plane of the Sun and direct westward. To clarify the interaction between the CME magnetic field and the solar wind motion, we assume that the background magnetic field of the solar wind is negligibly small, omitting the effect of the interplanetary magnetic field (IMF). We calculated the four different cases in which the toroidal and poloidal components of the spheromak magnetic field are respectively inverted. As the results of the simulations, we found that the toroidal and poloidal magnetic fluxes in the front torus of the spheromak shrink in the initial phase of the CME propagation when the CMEs keep fast speed. The results can be explained as the result that the magnetic fluxes in the front side of the spheromak are convected to the rear side of the CMEs by the interaction with the solar wind. It looks like the CME's internal magnetic structure is almost reversed along the propagation direction. After the initial phase, however, the magnetic structure of the interplanetary CMEs (ICMEs) is sustained during the propagation. The results suggest that the interaction with the solar wind may largely deform the ICME magnetic field mainly in the initial phase of propagation. Based on the simulations, we will discuss how the magnetic field of ICME can be deformed by the interactions with the solar wind and the IMF.