A theoretical study of the ionospheric F region equatorial anomaly—I. Theory☆

When observed noontime values of the maximum electron density, NMAX(F2), in the ionospheric F2 region are plotted as a function of magnetic latitude, a curve is produced which has two peaks, one on either side of the dip equator at ± 16° dip latitude. This paper theoretically investigates the daily variation of this latitudinal distribution of NMAX(F2) (the so-called Appleton or equatorial anomaly) and specifically attempts to account for the longitudinal differences observed between the American and Asian sectors. Part I outlines the theory involved in solving the time-dependent plasma continuity equation in which production, loss, and transport of ionization are taken into account, where the effects of neutral wind, ambipolar diffusion and E × B drift are included in the transport term. By describing the geomagnetic field in two equivalent ways, B = − ▽γ and B = ▽α × ▽β, where α, β and γ are known magnetic scalar potentials, the spherical r, θ and φ space coordinates of the continuity equation are transformed to coordinates which define directions parallel and perpendicular to the magnetic field thus putting the equation in a form suitable for numerical integration.