Ionospheric Modulation by Storm Time Pc5 ULF Pulsations and the Structure Detected by PFISR-THEMIS Conjunction

We investigate a significant duskside ionospheric density modulation in the Pc5 frequency band and related spatial structures during the storm on 28 May 2017. We take advantage of 3-D ionospheric observations by the PFISR and simultaneous magnetospheric in situ observations. Inversion of the density suggests that the Pc5 pulsations modulated precipitating electrons over a broad range of energies (~5–500 keV). Such strong electron precipitation likely caused a significant density modulation rate of ~8 and ionospheric Pedersen and Hall conductances to vary rapidly and peaked at ~70–100 S. The reflection coefficient was also substantially modulated between 0.5 and 0.9. Moreover, the observations by the multibeam PFISR and THEMIS E both reveal that the Pc5 pulsations propagated westward in the duskside region. It suggests that quasiperiodic activities in the nightside and subsequent duskward drifts were likely the source of the duskside Pc5 pulsations.