Measurements of ionospheric electron content by the lunar radio technique

Measurements of the Faraday rotation of lunar radio echoes on a frequency of 151 Mc/s are used to determine the time variation in the total ionospheric electron content. Absolute values of ionospheric electron content are determined from these measurements in conjunction with information on the electron content below the F2 peak computed from vertical-incidence sounding data. Diurnal, day-to-day, and seasonal variations in the total electron content are presented. The ratio na∶nb of the number of electrons above the F2 peak to that below is found to be in the order of 4 to 5 during three summer nights (June) before sunrise and about equal to 3 after sunrise. For two days in November the ratio na:nb is found to be equal to about three both before and after sunrise. Possibilities of inferring other characteristics of the upper ionosphere from observed variations in the total electron content are briefly discussed.