Ogo 2 and 4 VLF observations of the asymmetric plasmapause near the time of SAR arc events

Ogo 2 and Ogo 4 VLF data on plasmapause crossings were compared with SAR arc observations reported on September 29, 1967, and on October 31 and November 1, 1968. The positions of the plasmapause and SAR arcs were found to agree within ±1° in invariant latitude. Ogo 4 evidence from the 0900–2100 MLT (magnetic local time) plane showed that the known local-time asymmetry in plasmapause L value (evening maximum, dawn minimum) could explain some of the apparent motions of the arcs as viewed from ground stations. Some other details of the arc motions are apparently due to substorm-related convection events in the outer plasmasphere.