Ionospheric Electron Content in Subtropical Regions

Abstract

The observational studies on the ionospheric electron content in the subtropical regions are reviewed. It is found that the gross features of the equatorial anomaly in electron content, viz. its structure and diurnal development, are consistent, in all longitude sectors, with the anomaly in electron density in the topside and the bottom side. The general features of the diurnal and seasonal variations of the electron content as a function of latitude and solar activity are discussed. The electron content variations at Delhi and Hawaii, which have almost the same geomagnetic latitude and dip, but differ in geographic location by 7° of latitude, are compared. It is further noted that the annual variation in the electron content is pronounced whenever the seasonal anomaly is absent and the semiannual component dominates when the seasonal anomaly is present. The electron content distributions in northern and southern hemispheres are also compared. Electron content contours have been generated and presented for use as ionospheric inputs for estimating errors in satellite navigation systems.