Equatorial ionospheric electron density below the F2 peak

Abstract

True height profile analysis below the F2 peak was employed in this study. Diurnal, seasonal, and solar cycle variations in electron density were examined from 100 km up the F2 peak. Some results obtained for the equatorial region in the Indian and American sectors were confirmed in this study. The departure of the daytime electron density from that of a simple Chapman variation begins from an altitude of about 190 km at low solar activity and from 210 km at high solar activity. The midday minimum is observable from about 100 km below the F2 peak at low solar activity. It is noticeable from about 40 to 90 km below the F2 peak at high solar activity, except in April, when a postnoon peak is not developed. Most of the features observed find their explanation in the vertical E × B plasma drift variation.