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 F2 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 F2 region. Application of the equation of continuity shows that the F2 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 F2 ionization densities found in low latitudes, and the high values of h'F2 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 F2 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 F2 region is presented.