Region E and the S _q Current System

Abstract

THE equilibrium equation for the electron density N in a solar-controlled ionospheric region, such as normal region E, is, with the usual nomenclature: where χ is the solar zenith angle, α′ the effective recombination coefficient and v the vector drift velocity; q ₀ is proportional to the intensity of the solar ionizing radiation. The solution of this equation has been discussed by Martyn¹ and by Appleton and Lyon². At or near noon, , and if the movement term div(N v) is small, the critical frequency fE is related in a simple manner to χ, and we can write: K is a constant, n = 2p and for an isothermal region has the value 4 for recombination and 2 for attachment. In practice, it is found that the values of n deduced from the approximate equation (2) usually lie between 2 and 4, and this has been interpreted by most workers as evidence for a height gradient in the effective recombination coefficient or non-isothermal conditions in the layer. An alternative approach, and one which we adopt here, is to suppose that the apparent variations in n with time and place may result at least partly from neglect of the movement term div(N v).