Further Analogue Studies of the Ionospheric F Layer

The analogue computer described by Briggs and Rishbeth in 1961 is used to solve the continuity equation for electron density in the F region of the ionosphere, taking account of production, loss and vertical diffusion of ionization. Two atmospheric models are used, one with `complete mixing' of the neutral constituents and one with `diffusive separation'; for each of these, experiments are made with `large', `small' and `zero' coefficients of plasma diffusion. Studies of the diurnally varying electron distributions show that, just after sunrise, the increase of electron density is controlled mainly by photo-ionization. By mid-day, the layer approaches an equilibrium condition in which the height of the peak is controlled by diffusion and loss. In the models with zero diffusion coefficients, a peak of electron density is formed temporarily after sunrise but does not exist, at a finite height, at other times of the day or night. After sunset, diffusion and loss act in such a way as to establish a `stationary' layer which preserves its shape while it decays at a uniform rate. A possible equilibrium of the night F layer, maintained by downward flow of ionization from the exosphere, is also considered. A special study is made of the way in which the F layer responds to diurnal and eclipse variations in the ionizing radiation. At any height below the F2 peak, the behaviour of the layer is mainly determined by the local values of the production and loss rates; but in the upper part of the F layer, vertical `coupling' by diffusion is so strong that the variations of electron density closely follow those at the F2 peak and are independent of local rates of production or loss, or even of diffusion. In a further experiment, an attempt is made to simulate the non-linear loss process operative in the lower F region, and the resulting splitting of the layer into F1 and F2 components is demonstrated.