Some Measurements of Atmospheric Noise at High Frequencies

Measurements of atmospheric noise level have been made at a number of stations for periods up to four years. The frequencies used for the observations were 2.5, 5, 10, 15 and 20 Mc/s, and the method was based on the aural comparison of the received noise and a locally generated noise signal of controllable amplitude. Some of the results of these observations are presented in the form of median values for each month and for each hour of the day, together with figures indicating the degree of scatter about the median. A comparison is made between the data and the calculated values of noise level based on the concept that lightning discharges are the sole source of atmospheric noise. There is reasonable confirmation for local storms but not for those at medium and long distances, and it is apparent that the mechanism of noise generation is only partially understood. The overriding fact is that the characteristics of atmospheric noise at one location do not appear to be applicable over a large area, and other factors throw doubt on the concept of long-distance propagation of high-frequency noise. It is suggested tentatively that some noise sources may be quite local, but more experimental data are required to confirm or disprove this opinion.