High-Frequency Atmospheric Noise

A method which has been employed in the measurement of high-frequency atmospheric noise is described. Using this method measurements of noise over the range from 5 to 20 megacycles made in different parts of the United States and at different times of the year, show a distinct diurnal change in intensity similar to that for long-range high-frequency signal transmission. Except during periods of severe local disturbance noise on the lower frequencies is high during the night while on the higher frequencies the maximum occurs during the day. Simultaneous observation of crashes on different frequencies also suggests that the received atmospherics are largely transmitted by overhead paths. The variation in high-frequency atmospheric noise intensity during the passage of local electrical disturbance centers is shown. It is suggested that the intensity of atmospheric noise generated by these centers of electrical disturbance is inversely proportional to frequency. Measurement data are included showing the effect of sunrise and sunset, an eclipse of the sun, and disturbances in the earth's magnetic field upon the intensity of high-frequency atmospheric noise. Diurnal characteristics of high-frequency atmospheric noise on directive antennas facing England and South America and the noise reduction obtained by these arrays is illustrated. The possible location of distant centralized noise sources is discussed briefly.