Effect of the substorm phases on the electric field variation near the plasmapause inferred by the pulsation-pearl method

Abstract

The variation in the electric field near the night-side plasmapause was estimated in relation to the substorm phases by applying the PP method to dynamic spectra of the pearl-type Pc1 hydromagnetic waves observed at the low-latitude station, Onagawa. In order to clarify the relation between the electric field variation and the substorm phases, the beginning and the ending times of substorm expansion phase were defined by the onset time of low-latitude Pi 2 and from the hodograph of the substorm disturbance on the H-D plane, respectively. The convection electric field was found to increase westwards up to ~1.0mV/m during the expansion phase of substorm, changes its polarity near the end of the expansion phase, and then maintains eastwards during the recovery phase. The same conclusion was derived from the analysis of PP during a multiple-onset substorm, provided the words ‘expansion (or recovery) phase’ in the above conclusion are replaced by the words ‘individual expansion (or recovery) phase’.