Large-scale irregularities in the ionosphere

The amplitude of the 20-Mc/s signal from the satellite Explorer 7 was recorded at Auckland from November 1960 to August 1961. Variations in the fading period are used to study the irregularities that occur in the electron density of the ionosphere. Relations are given for calculating the size and density of these irregularities directly from plots of the fading period of the received signal. Results for 770 irregularities, observed at all times of day, with sizes from 5 to 500 km, are presented. The number with sizes between S and S+ΔS was approximately proportional to ΔS/S. The electron content of the irregularities, measured vertically, was generally between 0.03 and 4 per cent of the total electron content of the ionosphere, with a median value of 0.25 per cent. The density at the center of the irregularities differed from the density of the background ionization by about 1 per cent for the smaller and 10 percent for the largest ones. The irregularities were not elongated in the direction of the magnetic field, but occurred in the form of horizontal slabs with a vertical thickness equal to about one-fifth of the horizontal dimension. The fact that most irregularities larger than 50 km occurred in series of three or more similar ones suggests that they are caused by a wave of disturbance propagated through the ionosphere with a wavelength of about 100 km.