Horizontal Diffusion and the Geomagnetic Anomaly in the Equatorial F-Region

Abstract

MITRA¹ and others have suggested that horizontal ambipolar diffusion of ions and electrons may be of importance in the equatorial F-region, but there has been, so far as I know, no quantitative investigation of the rates of horizontal diffusion. Since diffusion will be almost exclusively parallel to the Earth's magnetic field, it is convenient for such an investigation to use orthogonal curvilinear co-ordinates based on the geomagnetic equipotentials and lines of force, and to introduce a co-ordinate, x, say, representing distance along a line of force, measured from a point vertically above the magnetic equator, at a distance a from the Earth's centre. If x, a and the height z are measured in units of the scale-height H, which is supposed constant, and if a dipole field is assumed, then I find that the rate of increase of electron density N due to diffusion at any point on a line of force is given by: except for some terms arising from the convergence of the lines of force which can usually be neglected. In this equation I is the magnetic dip, ψ the magnetic latitude and d₀ is a constant.