Some geomagnetic effects in the equatorial F2-region
The diurnal variations of the values of many ionospheric parameters obtained at Ibadan, Nigeria, close to the magnetic equator, are investigated on magnetically quiet days and on magnetically disturbed days. It is found that the midday minimum of the maximum concentration of ionization Nm in the F2 layer disappears as the days become more disturbed. On quiet days there is very little scatter of values of Nm, but on disturbed days this is much increased. Furthermore, both Nm and the total ion content, n, of a column of unit cross-section below the height of maximum ionization are greater at all times of the day on disturbed days than they are on quiet days. The perturbation of the quiet-day variation introduced on disturbed days, SD, has not only a diurnal (twenty-four hours) component, but also a semidiurnal component. Whilst there is general agreement in the behaviour of the results described here and the theory of ionospheric disturbances proposed by Martyn (1953), our data imply that the phases of the motions differ appreciably from those suggested by Martyn.