[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-P01] Multi-spacecraft observations of the magnetosphere and ionosphere under low Alfvén Mach number solar wind

*Masaki N Nishino¹、Yukinaga Miyashita^2,3、Motoharu Nowada⁴、Yoshifumi Saito¹ (1.Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science、2.Korean Astronomy and Space Science Institute、3.Korea National University of Science and Technology, Department of Astronomy and Space Science、4.Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Institute of Space Sciences)

キーワード：Solar wind Alfvén Mach number, Transpolar arc, Multi-satellite observations, Magnetosphere-Ionosphere coupling

The transpolar arcs (TPAs) appear in the auroral oval under the northward interplanetary magnetic field (IMF), sometimes accompanied by the change of the B_Y sign. Previous statistical studies showed that the solar wind magnetic field strength or the magnetic energy does not affect the occurrence of the TPAs. On the other hand, it has not been studied if the TPAs appear similarly when the solar wind density is very low, and thus, its Alfvén Mach number (M_A) is very low (~2-3). Here, we show a case study of multiple TPAs during high M_A solar wind observed by DMSP satellites, which was followed by TPA occurrence during very low M_A solar wind. The TPA under low M_A solar wind is typically single and faint, while multiple TPAs of complicated structures appeared in some cases. In this event, ARTEMIS P1 and P2 were in the mid-distant magnetotail in the same period, and their magnetopause crossings suggest a strong distortion of the magnetotail that might be related to the shape of the TPAs. We discuss the magnetosphere-ionosphere coupling under low M_A solar wind and northward IMF based on multi-spacecraft observations.