Generation region of pulsating aurora obtained simultaneously by the FAST satellite and a Syowa-Iceland conjugate pair of observatories

Abstract

We have carried out a direct comparison of pulsating auroras observed from the ground at Syowa Station in Antarctica and on board the FAST satellite (∼3100 km altitude), with reference to simultaneous data obtained by a Syowa-Iceland conjugate pair of observatories. The aurora at Syowa appeared as east-west aligned bands consisting of two different types: a poleward moving oscillation and a standing oscillation, each with a period of ∼6 s. Spatial and temporal variations of the downgoing high-energy (>5 keV) electron flux obtained by FAST showed a one-to-one correspondence with the optical pulsating aurora. The occurrence regions of the two different types of pulsating aurora were separated by a narrow gap (∼7-10 km in width at 100 km altitude) in the inverted-V structure, and the gaps were colocated with the small-scale upward field-aligned currents. The time-varying magnetic fields (upward field-aligned current) observed by FAST were almost correlated (in-phase) with the downgoing electron flux (>5 keV) modulations. Both the optical emission intensity at Syowa and the downgoing high-energy electron flux (>7 keV) on board FAST showed ∼3 Hz modulation. The ∼3 Hz fine structure constituted the main body of the ∼6 s pulsating aurora. VLF wave activities were not observed by FAST in the region of pulsating aurora. The source regions of the generation or modulation of the energetic particles are estimated to be at a higher altitude than FAST, in the region of ∼2 Re to 6 Re from the satellite. This suggests that the source region is not located in the equatorial plane of the magnetosphere but is located earthward, far from the equatorial plane. The conjugate pair observations on the ground revealed that the aurora, though pulsating in both hemispheres, was not conjugate in shape, appearing as an east-west aligned band in the Southern Hemisphere but as a torch structure (omega band) in the Northern Hemisphere. The evidence presented in this study suggests that ionosphere-magnetosphere coupling processes are important in producing the pulsating aurora. Copyright 2004 by the American Geophysical Union.