Diurnal power variations of the Earth-ionosphere cavity modes and their relationship to worldwide thunderstorm activity

Measurements of ELF radio-noise power in the lowest modes of the earth-ionosphere cavity were taken throughout 12 days during February 1961. The mean diurnal variation of the power in the first mode corresponds very closely to the mean worldwide thunderstorm activity expected for that month. Differences in the behavior of different modes can be explained on the basis of the differing geometrical configuration of the modes. Direct comparison with weather records reveals some correlation between day-to-day variations in noise power and thunderstorm activity. Finally, the measured powers are converted to absolute field strengths by use of a calibrated test signal.