Generation mechanism of Region 1 field-aligned current and energy transfer from solar wind to polar ionosphere

Field-aligned current (FAC) is of importance in energy transfer from space to the Earth. The Region 1 current, which flows in the polar region, is the most significant one, but the generation region and mechanism are long-lasting questions. By using the global magnetohydrodynamics (MHD) simulation, we traced packets of the Alfvén waves traveling parallel to the magnetic field in the rest frame of moving plasma. The low-latitude magnetospheric boundary layer is found to be the major generation region, where the plasma pulls newly reconnected magnetic field lines. The generation region is far from the original magnetic field lines extending from the Region 1 FAC in the ionosphere because of low Alfvén velocity in the outer magnetosphere and beyond. The Region 1 FACs are surrounded by the integral curves of the Poynting vector (called S-curve). The S-curve shows a helix with its center moving toward the Earth. The Region 1 FACs, circular motion of plasma (probably related to the magnetospheric convection), and transfer of magnetic energy to the Earth are closely related with each other. The new method can be widely applied to search for the generation region of FACs and useful for better understanding of the dynamics of the magnetosphere.