Diffusion of ionization in a dipole field

An equation is derived for the rate of ambipolar diffusion along lines of force in a dipole field; its significance is discussed, especially in relation to the magnitude and effects of horizontal outward diffusion in the ionosphere near the magnetic equator. At great heights the variation of electron density with reduced height z approximates at all latitudes to e−1/2 z. Upward electrodynamic drift at the equator can probably lead to a substantial reduction of peak electron density, owing to increased outward diffusion, as envisaged in the ‘fountain theory’ but only if the drift velocity is large in relation to the ambient recombinative loss rate.