Variations in the ionosphere during an aurora substorm as observed by an ionosonde

Abstract

In order to obtain a better understanding of the influence of precipitating electrons on the ionosphere, we tried to estimate their effect from ionosonde observation data (ionograms) during an aurora substorm. In this analysis we used 72 aurora substorm events identified from the geomagnetic variation for one year beginning from October 1st,1997. We have adjusted the time axis of the growth phase, the expansion phase, and the recovery phase of each event so that different events can be expressed on a common time axis. Observed ionogram data (fmin, ftEs, h'Es) are plotted on this normalized time axis and the features of the ionogram are examined in each phase. As a result, the mean values of fmin and ftEs increased, and the mean values of h'Es decreased from the growth phase to the expansion phase. We have concluded that there is a high possibility of an increase of the flux of 10-100keV precipitating electrons from the growth phase to the expansion phase.