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Free keywords:
Field-aligned currents; Solar illumination; Dipole tilt
Abstract:
In this study we investigate the longitudinal variations in the mean densities of field-aligned currents (FACs) at high latitudes in different seasons, by using high resolution magnetic field data from SWARM A and C satellites. Longitudinal variations are about a factor of 1.2~3.2 larger in the Southern Hemisphere than in the Northern Hemisphere. A tidal analysis is applied to FACs. D0 and DW2 are the dominant non-migrating components. DW2 is larger than D0 in summer and equinox. The longitudinal variations in solar illumination can explain D0 wave in FACs, with more solar illumination at near pole longitudes than at far-from-pole longitude. Factors like the geomagnetic field strength and dipole tilt angle might contribute to the observed DW2 features in FACs. The FACs simulated by the global ionosphere and thermosphere model only show D0 wave. The theoretical study reveals that the role of neutral wind is comparable to that of the electric field in the formation of D0 wave.
