Natural noise fields from 1 cps to 100 kc

Vertical electric
z
and horizontal magnetic rms noise field intensifies have recently been measured by the authors over the frequency range of 30 cps to 50 kc for all seasons of the year and for all time blocks. This data is combined with that of other workers in the field to present the natural noise density spectra from 1 cps to 100 kc for central United States regions. The portion of the data between 10 and 100 kc is found to be in close agreement with CCIR Report 65, "Revision of Atmospheric Radio Noise Data" [1]. Seasonal and diurnal variations at these locations are seen to become small below 1 kc. In addition to rms data, the authors measured the peak envelope occurring within 5-minute time intervals in a 7-cps bandwidth. Under certain conditions, rapid changes in the peak envelope to rms dynamic range were noted between 3 and 8 kc. This phenomenon is discussed with respect to source characteristics and propagation.