Global Characteristics of Improved Interhemispheric Field-Aligned Currents and of F-Region Meridional Currents Observed by the Swarm Dual-Spacecraft

The Swarm satellite constellation provides an excellent opportunity to explore ionospheric current systems. In this study, we have reanalyzed the ionospheric currents derived by the Swarm dual-satellite approach, to investigate the characteristic of inter-hemispheric field-aligned currents (IHFAC). One major improvement is that the influence of the ambient magnetic field on the IHFAC intensity has been taken into account, and the derived IHFAC densities are normalized to their ionospheric E-region footprints. In addition, we have extended the analysis to the middle latitudes within & PLUSMN;60 & DEG; MLat, which show IHFAC features different from those at low latitudes. For the first time the tidal features at mid-latitudes are studied. They are dominated by longitudinal wave-1 and wave-2 patterns. A superposition of these tidal components reflects a confinement of the IHFAC tidal modulation to daytime in the western hemisphere. The tidal signatures at middle latitudes are better organized in universal time than in local time. The strongest IHFACs are appearing around 18-19 UT, near noon in the American sector. This is related to the overlap with the South Atlantic Anomaly. For the first time we define and analyze the F-region meridional currents (FMC), interpreting the remaining part of the ionospheric radial current (IRC), which is not covered by IHFAC. The mean FMCs are found to be highly symmetric with respect to the magnetic equator and only amounts to one-third or half of the IHFAC density, however, they show neither typical longitudinal, diurnal variations, or tidal signatures.