Atmospheric tides in the ionosphere - I. Solar tides in the F 2 region

Abstract

A theory, based on solar tides, is advanced to explain the anomalous seasonal, diurnal and geographical variations of F 2 region ionization. It is shown that the horizontal winds due to these tides must cause electrons to move along the lines of the earth’s magnetic field. The resultant motion has a vertical component. Account is taken of polarization of the medium by the ‘dynamo’ electric forces. Owing to viscosity the vertical motion decreases upwards in the F 2 region. Application of the equation of continuity shows that the F 2 region becomes greatly distorted. A ‘longitude effect’ is found to arise by reason of the asymmetry of the earth’s magnetic field. The theory is used to explain the high F 2 ionization densities found in low latitudes, and the high values of h' F 2 at noon near the equator. It is also used to explain the afternoon and night-time increases in ionization found at certain locations. It is suggested that the effective recombination coefficient in F 2 is much lower than the generally accepted values. It is shown that Appleton & Weekes’s evidence of lunar tidal effects in the E region does not conflict with the ‘dynamo’ theory of magnetic variations or with Pekeris’s calculations. Observational evidence of the existence of solar tides in the F 2 region is presented.