A SIMPLE SPECTRAL MODEL OF F-REGION ELECTRON-DENSITIES AT EQUATORIAL AND LOW LATITUDES

Steady state plasma continuity equation for F-region of the earth's ionosphere at low latitudes has been solved by including plasma transport due to electromagnetic (E X B) drift and neutral winds. Electron densities are expressed analytically as a function of dip latitude using Legendre polynomials. Vertical equatorial drift velocity is used as an adjustable parameter so as to fit the ionospheric electron content measured at an equatorial anomaly station Rajkot (lat. 22.3-degrees-N, long. 70.7-degrees-E, dip lat. 16.5-degrees-N). Electron densities are calculated for solar maximum and minimum conditions, three seasons equinox, summer, winter), and three local times during day (0900, 1300, 1700 hrs). The set of Legendre expansion coefficients have been stored and can be used to generate electron density profiles at any dip latitude. The adjusted values of equatorial drift velocity are compared with the Doppler and incoherent radar measurements, and the results are discussed.