DAY-TO-DAY VARIABILITY IN IONOSPHERIC ELECTRON-CONTENT AT LOW LATITUDES

Published values of ionospheric electron content (IEC) are used to study its day-to-day variability at a number of low latitude stations in Indian, American and Pacific Sectors for varying levels of solar activity. It is seen that the variability is larger at night than day, higher in winter compared with summer and higher in low sunspot periods than in high sunspot periods. From a correlative study of variability in IEC with possible causative factors such as solar 10.7 cm flux, sunspot activity, magnetic activity and electrojet strength, it is seen that the dominant factor contributing to the variability in IEC is the electrojet strength at stations near the crest of the equatorial anomaly and the solar ionizing flux at the equatorial station. © 1990.