Direct contribution of oblique field-aligned currents to magnetic field variations on the ground

概要

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Attempt has been made to evaluate a direct contribution of the horizontal component of oblique field-aligned currents to surface magnetic variations in the auroral region associated with a localized electric potential distribution on the horizontal plane, in comparison with that of the ionospheric eddy current. This direct effect is proportional to a product of two ratios, the Pedersen to Hall conductivities and the horizontal to vertical components of the local dipole magnetic intensity. In addition to these, the shorter the horizontal scale-length in the east-west direction compared with that in the north-south direction, the larger the direct effect of field-aligned currents. For the localized perturbation with an isotropic horizontal structure at 60° geomagnetic latitude, it attains to about 80% of the magnetic contribution of the Hall current at the earth's surface. It is also shown that only the vertical component of oblique field-aligned currents connects with the irrotational part of ionospheric currents, and that the effective conductance in the magnetosphere for three-dimensional current systems is reduced to a smaller value than that for the case of vertical field lines.
国立極地研究所の論文