Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. On a worldwide scale, eight million lightning discharges per day — about 100 lightning flashes per second.

History

In 1925, AT&T Bell Laboratories started investigating the sources of noise in its transatlantic radio telephone service.
Karl Jansky

Karl Guthe Jansky

Karl Guthe Jansky was an American physicist and radio engineer who in August 1931 first discovered radio waves emanating from the Milky Way. He is considered one of the founding figures of radio astronomy.- Early life :...

, a 22 year old researcher undertook the task. 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. 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

Cosmic noise

Cosmic noise and galactic radio noise is random noise that originates outside the Earth's atmosphere. It can be detected and heard on radio receivers.- Elaboration :Cosmic noise characteristics are similar to those of thermal noise...

 from the center of the Milky Way

Milky Way

The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

. Jansky's research made him the father of radio astronomy

Radio astronomy

Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...

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Lightning

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 for cloud-to-cloud flashes. On a worldwide scale, eight million lightning flashes occur daily. This is about 100 lightning flashes per second.

The sum of all these lightning flashes results in atmospheric noise. It can be observed with a radio receiver in the form of a combination of white noise

White noise

White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...

 (coming from distant thunderstorms) and impulse noise

Impulse noise

Impulse noise could mean:*impulse noise *Electromagnetic interference*Burst noise...

 (coming from a near thunderstorm). The power-sum varies with seasons and nearness of thunderstorm centers.

Although lightning has a broad-spectrum emission, its noise power increases with decreasing frequency. Therefore, at Very Low Frequency

Very low frequency

225px|thumb|right|A VLF receiving antenna at [[Palmer Station]], Antarctica, operated by Stanford UniversityVery low frequency or VLF refers to radio frequencies in the range of 3 kHz to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals...

 and Low frequency

Low frequency

Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...

, atmospheric noise often dominates, while at High Frequency

High frequency

High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...

, man-made noise dominates in rural areas.

Survey

From 1960s to 1980s, a worldwide effort was made to measure the atmospheric noise and variations. This has been documented in the CCIR

ITU-R

The ITU Radiocommunication Sector is one of the three sectors of the International Telecommunication Union and is responsible for radio communication....

322 publication. CCIR 322 provided seasonal world maps showing the expected values of the atmospheric noise figure F_a at 1 MHz during four hour blocks of the day. Another set of charts relates the F_a at 1 MHz to other frequencies. CCIR Report 322 has been superseded by ITU P.372 publication.

Random number generation

Atmospheric noise and variation is also used to generate high quality random numbers. Random numbers have interesting applications in the security domain.