Confirmation of Small Scale Field-Aligned Currents in Middle and Low Latitudes and an Estimation of Their Typical Period of Temporal Variation

From the analysis of the data obtained by the Oersted and CHAMP satellites, we found that the small-scale magnetic fluctuations with amplitude about a few nT or less having apparent period along the satellite orbit about 10-30 seconds exist almost always. From their statistical characteristics, we suppose that their origin is in the lower atmosphere (Nakanishi et al., 2014). In this paper, we present a clear evidence that the magnetic fluctuations are the spatial structures of small scale field-aligned currents along satellite orbit. By using the data obtained during initial one month when the SWARM-A and SWARM-B were flying on almost the same orbit with gradually increasing separation, we try to estimate the temporal scale of variation of the field-aligned currents. We compare the period with the possible magnetic signature of the field-aligned current system observed on the ground.