Natural and man-made terrestrial electromagnetic noise: an outlook

Natural electromagnetic noise sources existing since the origin of the Earth may be influencing the evolution of living systems. Understanding how this background noise is generated and distributed and how it interacts with living systems, can contribute to the general knowledge of life on Earth. In this review we consider the different frequency ranges, starting from the lowest frequencies generated within the ionospheric and magnetospheric cavities, up to the microwave band, including galactic noise, for both natural and man-made noise. Different sources generate natural noise inside the magnetospheric cavity at different frequencies. A primary source of noise is given by the interaction of particles and waves coming from outer space with the magnetosphere plasma at various altitudes; another source is inside the ionospheric cavity where atmospheric lightning discharges produce several interesting propagating phenomena. At higher frequency radio noise originated in the atmosphere becomes less important and cosmic noise is prevalent up to the millimetric wavelength. Human technologies implanted for power transmission and communications are the well known causes of man made noise. Man-made noise, mainly due to communication and broadcasting systems, electric energy transport systems, automotive ignition, industrial thermal processes and instruments for scientific/medical appliances is distributed, albeit not uniformly, in all bands. In VLF-HF band atmospheric noise is still larger than man-made noise in the order of a tenth of dB in rural areas and Natural and man-made terrestrial electromagnetic noise: an outlook