Abstract
Abstract. Recently, a model of large-scale, field-aligned current (FAC) structures, based on zero-frequency MHD surface wave (SW) modes that can emerge from the solar wind-Earth's magnetosphere interaction, has been proposed. The FAC polarity and intensity distribution are quantified as a function of the solar wind parameters and the interplanetary magnetic field (IMF) magnitude that enter as input parameters. Besides, there are input parameters intrinsic to the Earth's magnetosphere – the size of the polar cap and the boundary regions and their plasma density variations. Influence of the IMF By component on the FAC structure is examined here. Depending on the IMF By magnitude, the predicted six-cell FAC structure tends to evolve in a spiral-like fashion. This large-scale FAC model is compared with experimental evidences and empirical FAC models based on DE-2 satellite data and high-precision Oersted and Magsat satellite magnetometer data. Among the various achievements of these long-term satellite measurements, an observation/discovery of a ground-based state of FACs which includes a pair of large-scale FACs in the polar cap under both positive and negative IMF Bz has been pointed out. The FAC pattern is qualitatively and quantitatively consistent with experimental data for both polar cap FAC and Region 1 and Region 2 FAC systems.
Highlights
Large-scale, field-aligned currents (FACs), known as Birkeland currents (Potemra, 1985), represent a substantial part of the electric current systems that support the Earth’s magnetosphere structure during its dynamic interaction with the solar wind variations
Taking the Pedesen conductance p values of 10 S we found that a convective electric field magnitude of 20 mV/m can initiate multiple FAC/electric field structures
The principal issues that follows from the suggested surface wave (SW) mode FAC model are i) the large-scale FAC intensity and distribution in the polar ionosphere can be quantified provided that the solar wind, interplanetary magnetic field (IMF) and magnetospheric parameters are known
Summary
Large-scale, field-aligned currents (FACs), known as Birkeland currents (Potemra, 1985), represent a substantial part of the electric current systems that support the Earth’s magnetosphere structure during its dynamic interaction with the solar wind variations. When the interplanetary magnetic field (IMF) component Bz is positive, i.e. northward, a pair of FACs of inversed polarity poleward of the Region 1 (i.e. in the polar cap region) has been found (Iijima et al, 1984; Zanetti et al, 1984; Stauning, 2002). The latter is referred to as Northward Bz (NBZ) FAC systems. A three-sheet FAC system that includes cusp (or Region 0), Region 1 and Region 2 currents on the dayside may exist simultaneously (Erlandson et al, 1988) These largescale FAC systems have typical intensities of ∼1 μA/m2 at ionospheric heights
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