A Model Electron-Density Profile for Noontime Equatorial Lower Ionosphere

Abstract

D- and E- region electron-density profiles over Colombo (lat., 06° 54'N) have been deduced by using AI-absorption data at frequencies 2.0, 2.2 and 2.6 MHz spread over half a solar cycle during 1964-68. The noontime absorption data, normalized with respect to zenith angle and solar activity variations are subjected to harmonic analysis. The mean value obtained in the harmonic analysis is taken as the absorption value at the frequency freed from all seasonal, zenith angle and solar activity effects. In deriving the electron-density distribution, an arbitrary electron-density profile computed from well-known production and loss processes in the lower ionosphere is first considered and then this profile is adjusted by trial and error until the computed values of absorption and virtual height, using the generalized Sen-WyIler theory, are in good agreement with the noontime mean values mentioned at all the frequencies. Further, in regard to the seasonal variation of absorption at Colombo, it is found that the semi-annual component is the dominant one and its phase agrees remarkably with the phase of the semi-annual osciIlation of the air density in the lower thermosphere.