[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-01] Region 1型沿磁力線電流の生成領域

*海老原 祐輔¹、田中 高史 (1.京都大学生存圏研究所)

キーワード：沿磁力線電流、太陽風ー磁気圏ー電離圏結合

We propose a new approach for identifying the origin of Region 1 field-aligned currents (FACs) by taking into account Alfvén traveling time and background motion of plasma. Using global magnetohydrodynamics (MHD) simulation for steady and purely southward interplanetary magnetic field (IMF), we introduce 'packets' that are supposed to carry the perturbations associated with FACs, and trace them backward in time from the center of the upward Region 1 FAC at the ionospheric altitude. Flank (low-latitude) magnetopause is identified to be a major generator region, in which solar wind-originated plasma pulls the newly reconnected magnetic field lines. The newly reconnected magnetic field line accelerates magnetosphere-originated plasma. As the magnetosphere-originated plasma propagates downward, it further pulls the magnetic field line, generating in the generation of the Region 1 FAC. The involvement of the reconnection can explain the general dependence of the intensity of the Region 1 FAC on the southward IMF. The generation of Region 1 FACs is caused by the field-aligned gradient of space charge ∇_||(∇×E), where E is the electric field, and the contribution from the term (∇²E)_||. The latter one is nonnegligible because of curved magnetic field lines. The generation processes are fully different from those previous suggested. The flank generator can reasonably explain the latitudinal and the longitudinal extent of the Region 1 FACs because of the finite travel time of the Alfvén waves under convective motion.