Whistler (radio)
Encyclopedia
A whistler is a very low frequency
electromagnetic (radio) wave
which can be generated, for example, by lightning
. Frequencies of terrestrial whistlers are 1 to 30 kHz, with maximum usually at 3 to 5 kHz. Although they are electromagnetic waves, they occur at audio frequencies
, and can be converted to audio using a suitable receiver. They are produced by lightning strikes (mostly intracloud and return-path) where the impulse travels away from the earth and returns to the earth traveling along magnetic field lines. They undergo dispersion
of several thousand kHz due to the slower velocity of the lower frequencies through the plasma
environments of the ionosphere
and magnetosphere
. Thus they are perceived as a descending tone which can last for a few seconds. The study of whistlers allows categorization into Pure Note Whistlers, Diffuse, 2-hop, and Echo Train types.
In addition, Voyager 1
and 2 spacecraft detected whistler like activity in the vicinity of Jupiter
, implying the presence of lightning there.
wave guide is known as a sferic. If the signal is injected through the ionosphere and allowed to propagate through the magnetosphere, the signal is now prone to a bounce-mode propagation, reflecting back and forth on opposite sides of the planet until totally attenuated. To clarify which part of this hop pattern the signal is in, it is specified by a number, indicating the portion of the bounce path it is currently on. On its first upward path, it is known as a 0+. After passing the geomagnetic equator, it is referred to as a 1-. The + or - sign indicates either upward, or downward, propagation, respectively. The numeral represents the half-bounce currently in progress. The reflected signal is redesignated 1+, until passing the geomagnetic equator again; then it is called 2-, and so on.
Originally published by Stanford University Press, Stanford, California (1965). See also Whistlers and VLF Emissions by the same author. (These are best sought in a library)
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...
electromagnetic (radio) wave
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
which can be generated, for example, by lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
. Frequencies of terrestrial whistlers are 1 to 30 kHz, with maximum usually at 3 to 5 kHz. Although they are electromagnetic waves, they occur at audio frequencies
Audio frequency
An audio frequency or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human...
, and can be converted to audio using a suitable receiver. They are produced by lightning strikes (mostly intracloud and return-path) where the impulse travels away from the earth and returns to the earth traveling along magnetic field lines. They undergo dispersion
Dispersion
Dispersion may refer to:In physics:*The dependence of wave velocity on frequency or wavelength:**Dispersion , for light waves**Dispersion **Acoustic dispersion, for sound waves...
of several thousand kHz due to the slower velocity of the lower frequencies through the plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
environments of the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
and magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
. Thus they are perceived as a descending tone which can last for a few seconds. The study of whistlers allows categorization into Pure Note Whistlers, Diffuse, 2-hop, and Echo Train types.
In addition, Voyager 1
Voyager 1
The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...
and 2 spacecraft detected whistler like activity in the vicinity of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, implying the presence of lightning there.
History
The existence of whistlers was first noticed by Barkhausen in 1918. In 1953, Storey explained the origin of them, showing that whistlers are originated by lightning discharges.Nomenclature
The propagation of a signal in the Earth IonosphereIonosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
wave guide is known as a sferic. If the signal is injected through the ionosphere and allowed to propagate through the magnetosphere, the signal is now prone to a bounce-mode propagation, reflecting back and forth on opposite sides of the planet until totally attenuated. To clarify which part of this hop pattern the signal is in, it is specified by a number, indicating the portion of the bounce path it is currently on. On its first upward path, it is known as a 0+. After passing the geomagnetic equator, it is referred to as a 1-. The + or - sign indicates either upward, or downward, propagation, respectively. The numeral represents the half-bounce currently in progress. The reflected signal is redesignated 1+, until passing the geomagnetic equator again; then it is called 2-, and so on.
Related Topics
- Dawn chorus (electromagnetic)Dawn chorus (electromagnetic)The electromagnetic dawn chorus is an unexplained phenomenon that occurs most often at sunrise or shortly after, that resembles the sound of the birds' dawn chorus. Chorus is believed to be generated by a Doppler-shifted cyclotron interaction between anisotropic distributions of energetic ...
- electromagnetic electron waveElectromagnetic electron waveAn electromagnetic electron wave is a wave in a plasma which has a magnetic field component and in which primarily the electrons oscillate.In an unmagnetized plasma, an electromagnetic electron wave is simply a light wave modified by the plasma...
- Hiss (electromagnetic)Hiss (electromagnetic)Electromagnetic hiss is a naturally occurring Extremely Low Frequency/Very Low Frequency electromagnetic wave that is generated in the plasma of either the Earth's ionosphere or magnetosphere...
- Atmospheric noiseAtmospheric noiseAtmospheric 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:...
- Radio atmosphericRadio atmosphericA radio atmospheric signal or sferic is a broadband electromagnetic impulse that occurs as a result of natural atmospheric lightning discharges. Sferics may propagate from their lightning source without major attenuation in the Earth-Ionosphere waveguide, and can be received thousands of...
Relevant Spacecraft
- Advanced Composition ExplorerAdvanced Composition ExplorerAdvanced Composition Explorer is a NASA space exploration mission being conducted as part of the Explorer program to study matter in situ, comprising energetic particles from the solar wind, the interplanetary medium, and other sources. Real-time data from ACE is used by the Space Weather...
(ACE), launched 1997, still operational. - Helios (spacecraft)
- MESSENGERMESSENGERThe MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury...
(MErcury Surface, Space ENvironment, GEochemistry and Ranging), launched 2004, still operational. - Radiation Belt Storm ProbesRadiation Belt Storm ProbesThe Radiation Belt Storm Probes is a NASA mission under the Living With a Star program. The goal of the LWS program is to develop the scientific understanding necessary to effectively address those aspects of the connected Sun-Earth system that directly affect life and society...
- Solar Dynamics ObservatorySolar Dynamics ObservatoryThe Solar Dynamics Observatory is a NASA mission which will observe the Sun for over five years. Launched on February 11, 2010, the observatory is part of the Living With a Star program...
(SDO), launched 2010, still operational. - Solar and Heliospheric ObservatorySolar and Heliospheric ObservatoryThe Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...
(SOHO), launched 1995, still operational. - Solar Maximum MissionSolar Maximum MissionThe Solar Maximum Mission satellite was designed to investigate solar phenomenon, particularly solar flares. It was launched on February 14, 1980....
(SMM), launched 1980, decommissioned 1989. - Solar OrbiterSolar OrbiterSolar Orbiter is a planned Sun-observing satellite, under development by the European Space Agency . The main mission scenario is a launch by an Atlas V from the Kennedy Space Center in Florida in January 2017...
(SOLO), set to launch in 2015. - Solar Probe Plus, set to launch in 2015.
- STEREOSTEREOSTEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
(Solar TErrestrial RElations Observatory), launched 2006, still operational. - Transition Region and Coronal Explorer (TRACE), launched 1998, decommissioned 2010.
- Ulysses (spacecraft), launched 1990, decommissioned 2009.
- WIND (spacecraft), launched 1994, still operational.
Further reading
- A site containing recorded audio of natural VLF phenomena.
- A beginner's guide to natural VLF radio phenomena - second part.
- Natural VLF Radio - Whistlers.
Originally published by Stanford University Press, Stanford, California (1965). See also Whistlers and VLF Emissions by the same author. (These are best sought in a library)