Atmospheric noise
Atmospheric noise is radio noise, or "static", caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. On a worldwide scale, there are about 40 lightning flashes per second, or ≈ 3.5 million lightning discharges per day.[2]
Lightning
[edit]Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. It is mainly caused by cloud-to-ground flashes as the current is much stronger than that of cloud-to-cloud flashes.[2] On a worldwide scale, 3.5 million lightning flashes occur daily. That means there are about 40 lightning flashes per second.[3]
The sum of all these lightning flashes results in atmospheric noise. It can be easily heard with any AM radio or SSB receiver tuned to an unused frequency.[4] The heard static is a combination of white noise (cumulative of distant thunderstorms) and impulse noise (from relatively nearby thunderstorms, if any). The power-sum varies with seasons and nearness of thunderstorm centers. It can be seen as random speckles on an old analog TV set dialed to an empty channel.
Although lightning has a broad-spectrum emission, its noise power increases with decreasing frequency. Therefore, at very low frequency and low frequency, atmospheric noise often dominates, while at high frequency, man-made noise dominates in urban areas.
History
[edit]Early investigation and study
[edit]In 1925, AT&T Bell Laboratories started investigating the sources of noise in its transatlantic radio telephone service.[5](pp 402–408)
Then a 22 year-old researcher, K.G. Jansky undertook the task in 1928. By 1930, a radio antenna for a wavelength of 14.6 meters was constructed in Holmdel, NJ, to measure the noise in all directions. Jansky recognized three sources of radio noise:[5](pp 404–405)
- The first (and strongest) source was local thunderstorms.
- The second source was weaker noise from more distant thunderstorms.
- The third source was a still weaker hiss that turned out to be galactic noise from the center of the Milky Way.
Jansky's research made him the "father of radio astronomy".[5](p 406)
In early 1950s, S.V.C. Aiya published a mathematical model of the cumulative effects of lightning and thunderstorms on broadcasting.[6]
Later survey data
[edit]From 1960s to 1980s, a worldwide effort was made to measure the atmospheric noise and variations. Results have been documented in CCIR Report 322.[1][7] CCIR 322 provided seasonal world maps showing the expected values of the atmospheric noise figure Fa at 1 MHz during four hour blocks of the day. Another set of charts relates the Fa at 1 MHz to other frequencies. CCIR Report 322 has been superseded by publication of ITU R-RE-P.372.[8]
Random number generation
[edit]Atmospheric noise and variation is also used to generate high quality random numbers. Random numbers have crucial applications in the security domain.[9]
See also
[edit]References
[edit]- ^ a b Characteristics and Applications of Atmospheric Radio Noise Data (Report). International Radio Consultative Committee (CCIR). Geneva, CH: International Telecommunication Union (ITU). 1968. CCIR Report 322-3.; first CCIR Report 322 was 1963; revised first ed.; second is ISBN 92-61-01741-X.
- ^ a b "Annual lightning flash rate map". Science on a Sphere. sos.noaa.gov. Datasets. National Oceanographic and Atmospheric Administration (NOAA). Archived from the original on 24 March 2014. Retrieved 15 May 2014.
- ^ Spaulding, Arthur D.; Washburn, James S. (April 1985). Atmospheric Radio Noise: Worldwide levels and other characteristics (Report). NASA Sti/Recon Technical Report N. Vol. 86. Boulder, CO: U.S. Department of Commerce, National Telecommunications & Information Administration, Institute for Telecommunications Sciences. p. 13639. Bibcode:1985STIN...8613639S. NTIA Report TR-85-173.
- ^ Sample of atmospheric noise. ycars.org (audio recording). York County, PA: York County Amateur Radio Society. Archived from the original (MP3) on 18 December 2005. Retrieved 14 March 2008.
- ^ a b c Singh, Simon (2005). Big Bang: The Origin of the Universe. Harper Perennial. ISBN 978-0-00-716221-5.
- ^ Aiya, S.V.C. (December 1956). "Noise radiation from tropical thunderstorms in the standard broadcast band". Nature. 178 (4544): 1249. Bibcode:1956Natur.178.1249C. doi:10.1038/1781249a0. S2CID 186242557.
- ^
Lawrence, D.C. (June 1995). Noise Variation Parameters. CCIR Report 322 (Report). San Diego, CA: U.S. Naval Command, Control and Ocean Surveillance Center, RDT&E Division. NRaD Technical Document 2813. Archived from the original on 13 November 2009.
- alt source
- ^ Radio Noise (Report). ITU Recommendation. Geneva, CH: International Telecommunication Union (ITU). R-RE-P.372 – via ITU.int.
- ^ Haahr, Mads. "Introduction to randomness and random numbers". random.org (self-published). Retrieved 14 November 2011.