Ionospheric disturbances at the equatorial anomaly crest region during the March 1989 magnetic storms

Abstract

On March 6,1989, the largest sunspot group since 1982 came into view as it moved out of the eastern limb of the Sun. It was highly active during March 8–18, and a great many transient ionospheric and geomagnetic variations were triggered by this sunspot group. The intensive ionospheric observations at Lunping Observatory and Chungli Ionosphere Station during this period recorded 30 solar flares manifested as shortwave fade‐outs, sudden frequency deviations, and solar flare effects and three storm sudden commencement (SSC)‐type geomagnetic storms, among which the March 13 SSC‐type geomagnetic storm triggered an unusually severe ionospheric disturbance. The ionospheric total electron content, the critical frequency of the F 2 layer, f 0 F 2 , and the virtual heights at given frequencies all show wavelike up‐and‐down oscillations of the ionosphere. This oscillatory ionospheric motion is explained as due to the compression and expansion of the plasmasphere.