DAY-TO-DAY VARIABILITY IN IONOSPHERIC ELECTRON-CONTENT

Published values of ionospheric electron content (IEC) are used to study its day-to-day variability at a number of stations extending from equatorial to mid-latitudes in Indian and American sectors for high and low solar activity years. It is seen that the variability is larger at night than by day, highest in February and November (D months) and lowest in equinox (E) months. The solar activity dependence is such that the variability is higher during high sunspot years than during low sunspot years for mid- and subauroral latitudes while for low latitudes this trend is reversed from 08 to 23 h local time. From a correlative study of the variability in IEC vis-a-vis that in possible causative factors such as solar 10.7 cm flux, magnetic activity, equatorial and auroral electrojet, the relative contributions of the above factors to the variability in IEC at different locations are brought out. The spatial correlation of TEC is also studied.