Gradual penetration of IMF By-component into the cusp and associated field-aligned current
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概要
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A transitional model is proposed to show how a pair of field-aligned currents is generated by IMF B_y-component in the cusp region. It is based on the idea of magnetic induction which has a relation to the magnetic shielding current. Originally, the current system which shields out IMF B_y-component from the earth's magnetosphere flows along the magnetopause-boundary layer. However, since the solar plasma can go through the high-latitude magnetopause, the current system can enter into the entry layer. When the current system arrives at a highaltitude cusp where the solar plasma flows away toward the plasma mantle, the magnetic disturbance accompanied by the shielding current begins to descend independently of the solar plasma flow. As it descends, the MHD frozen-in condition becomes satisfied and a magnetic disturbance perpendicular to the geomagnetic field propagates along the cusp field lines as an traveling rotational discontinuity. On the trail of the magnetic disturbance, field-aligned currents remain at both low-latitude and high-latitude sides of the cusp as stationary rotational type discontinuities with weak normal component of magnetic field. When the magnetic disturbance reaches the ionosphere, the descent stops and a quasisteady state is achieved. In this state, the magnetic shielding current on the surface of the traveling discontinuity turns to the ionospheric Pedersen current. Thus, the current circuit of a pair of cusp field-aligned currents and the ionospheric Pedersen current can be formed as a consequence of the entrance of the constant shielding current system on the solar sector boundary.
- 国立極地研究所の論文