国際発表 | 11th Toki Conference

Spontaneous Variation in a Rotating Magnetosphere

Takahiro Miyoshi^a and Kanya Kusano^b
a) Japan Atomic Energy Research Institute, Naka, Ibaraki 311-0193, Japan
b) Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan

Abstract.
The spontaneous variation of the spatio-temporal structure in a rotating magnetospheric system interacting with the external plasma flow is investigated by using the global magnetohydrodymamic (MHD) simulation. The results of the simulation indicate that the global structure of the magnetopause at the prenoon region, where the rotating plasma flow in the magnetosphere collides with the external flow, is varied spontaneously even when the condition of the external flow is steady. Especially in the case that the dynamic pressure of the external flow is relatively low, a sequence of slow expansion and rapid shrinkage of the prenoon magnetopause is recurrent, though the prominent fluctuation of the prenoon magnetopause cannot be observed in the high dynamic pressure case. The difference of their results may arise from the fact that, in the former case, the internal state in the rotating magnetosphere shows the dynamically dominant state, while the internal state is magnetically dominant over the day side region in the latter case. The mechanism of the spontaneous variation in the low dynamic pressure case is considered to be caused by the complicated nonlinear interaction between the external plasma flow, the rotating plasma flow in the magnetosphere, and the stress of the accumulated magnetic field lines at the prenoon magnetopause where the flow is almost stagnant.