Solution of the coupled ion and neutral air equations of the mid-latitude ionospheric F2-layer

Abstract

The time-dependent momentum and continuity equations for the ions and the time-dependent momentum equation for the neutral air are solved simultaneously for midlatitude F2-region conditions. In both momentum equations the non-linear acceleration terms are omitted. The pressure gradients in the neutral air are derived from Jacchia atmospheric models; also included in the neutral air momentum equation are ion drag, Coriolis and viscous forces. It is shown that, compared with the results of Geisler (1967), in whose calculations only the neutral air momentum equation was solved, the phases of the neutral air wind velocities are little affected by the feedback interaction between the ion and neutral air equations but the magnitudes of the velocities are different. When the peak electron concentration N m F2 falls below 10 5 cm −3, as it does at night, the wind velocities are determined by viscosity and Coriolis forces rather than by ion drag. The zonal wind has a small prevailing eastward component, much less than the observational value given by King-Hele and Scott (1967). With the values of the parameters used in these calculations (appropriate to sunspot minimum conditions), the behaviour of N m F2 by day is not the same as that usually observed. Variations of the coefficient of viscosity, the ion loss coefficient and the ion-neutral collision frequency give results that demonstrate the effects of feedback between the equations. At night, because the ionization is raised by an equatorward wind, N m F2 may remain almost constant for several hours before dawn, though its value is less than is normally observed.