Atmosphärische Elektrizität

Cloud to ground lightning in the global atmospheric electrical circuit. This is an example of plasma present at Earth's surface. Typically, lightning discharges 30,000 amperes, at up to 100 million volts, and emits light, radio waves, x-rays and even gamma rays . Plasma temperatures in lightning can approach 28,000 kelvins and electron densities may exceed 10²⁴/m³.

Atmospheric electricity is the study of electrical charges in the Earth's atmosphere (or that of another planet). The movement of charge between the Earth's surface, the atmosphere, and the ionosphere is known as the global atmospheric electrical circuit. Atmospheric electricity is an interdisciplinary topic, involving concepts from electrostatics, atmospheric physics, meteorology and Earth science.

Thunderstorms act as a giant battery in the atmosphere, charging up the ionosphere to about 400,000 volts with respect to the surface. This sets up an electric field throughout the atmosphere, which increases with altitude from about 100 V/m at the surface.

Atmospheric electricity involves both thunderstorms, which create lightning bolts that 'instantaneously' discharge huge amounts of atmospheric charge to ground in a rapid release of energy stored in the electric field that builds up in storm clouds, with a related phenomenon of continual electrification (re-charging) of the air in the lower atmosphere due to ionisation from cosmic rays and natural radioactivity.

History

Vorlage:Main article The detonating sparks drawn from electrical machines and from Leyden jars suggested to the early experimenters, Hauksbee, Newton, Wall, Nollet, and Gray, that lightning and thunder were due to electric discharges. In 1708, Dr. William Wall was one of the first to observe that spark discharges resembled miniature lightning, after observing the sparks from a charged piece of amber.

In the middle of the 18th century, Benjamin Franklin's experiments showed that electrical phenomena of the atmosphere were not fundamentally different from those produced in the laboratory. By 1749, Franklin observed lightning to possess almost all the properties observable in electrical machines.

In July 1750, Franklin hypothesized that electricity could be taken from clouds via a tall metal aerial with a sharp point. Before Franklin could carry out his experiment, in 1752 Thomas-François Dalibard erected a Vorlage:Convert iron rod at Marly-la-Ville, near Paris, drawing sparks from a passing cloud. With ground-insulated aerials, an experimenter could bring a grounded lead with an insulated wax handle close to the aerial, and observe a spark discharge from the aerial to the grounding wire. In May 1752, Dalibard affirmed that Franklin's theory was correct.

Franklin listed the following similarities between electricity and lightning:

• producing light of a similar color;
• rapid motion;
• being conducted by metals, water and ice;
• melting metals and igniting inflammable substances;
• "sulfurous" smell (which is now known to be due to ozone);
• magnetizing needles;
• the similarity between St. Elmo's Fire and glow discharge.

Around June 1752, Franklin reportedly performed his famous kite experiment. The kite experiment was repeated by Romas, who drew from a metallic string sparks Vorlage:Convert long, and by Cavallo, who made many important observations on atmospheric electricity. L. G. Lemonnier (1752) also reproduced Franklin's experiment with an aerial, but substituted the ground wire with some dust particles (testing attraction). He went on to document the fair weather condition, the clear-day electrification of the atmosphere, and the diurnal variation of the atmosphere's electricity. G. Beccaria (1775) confirmed Lemonnier's diurnal variation data and determined that the atmosphere's charge polarity was positive in fair weather. H. B. Saussure (1779) recorded data relating to a conductor's induced charge in the atmosphere. Saussure's instrument (which contained two small spheres suspended in parallel with two thin wires) was a precursor to the electrometer. Saussure found that the fair weather condition had an annual variation, and found that there was a variation with height, as well. In 1785, Coulomb discovered the electrical conductivity of air. His discovery was contrary to the prevailing thought at the time, that the atmospheric gases were insulators (which they are to some extent, or at least not very good conductors when not ionized). His research was, unfortunately, completely ignored. P. Erman (1804) theorized that the Earth was negatively charged. J. C. A. Peltier (1842) tested and confirmed Erman's idea.

Atmospheric electricity utilization for the chemical reaction in which water is separated into oxygen and hydrogen.

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Vion, Vorlage:US patent, "Improved method of using atmospheric electricity ('Electric Apparatus')", June 1860.

Several researchers contributed to the growing body of knowledge about atmospheric electrical phenomena. Francis Ronalds began observing the potential gradient and air-earth currents around 1810, including making continuous automated recordings. He resumed his research in the 1840s as the inaugural Honorary Director of the Kew Observatory, where the first extended and comprehensive dataset of electrical and associated meteorological parameters was created. He also supplied his equipment to other facilities around the world with the goal of delineating atmospheric electricity on a global scale. Kelvin's new water dropper collector and divided-ring electrometer were introduced at the Kew Observatory in the 1860s, and atmospheric electricity remained a speciality of the observatory until its closure. For high-altitude measurements, kites were once used, and weather balloons or aerostats are still used, to lift experimental equipment into the air. Early experimenters even went aloft themselves in hot-air balloons.

H. H. Hoffert (1888) identified individual lightning downward strokes using early cameras and would report this in "Intermittent Lightning-Flashes". J. Elster and H. F. Geitel, who also worked on thermionic emission, proposed a theory to explain thunderstorms' electrical structure (1885) and, later, discovered atmospheric radioactivity (1899) from the existence of positive and negative ions in the atmosphere. F. Pockels (1897) estimated lightning current intensity by analyzing lightning flashes in basalt (c. 1900) and studying the left-over magnetic fields. Discoveries about the electrification of the atmosphere via sensitive electrical instruments and ideas on how the Earth's negative charge is maintained were developed mainly in the 20th century, with CTR Wilson playing an important part. Current research on atmospheric electricity focuses mainly on lightning, particularly high-energy particles and transient luminous events, and the role of non-thunderstorm electrical processes in weather and climate.

Nikola Tesla and Hermann Plauson investigated the production of energy and power via atmospheric electricity. Tesla also proposed to use the atmospheric electrical circuit to transceive wireless energy over large distances, but no feasible apparatus to extract energy from atmospheric electricity has been built.

Description

Atmospheric electricity is always present, and in general, during fine weather, the air above the surface of Earth is positively charged, while the Earth's surface charge is negative.

The measurements of atmospheric electricity can be seen as a difference of potential between a point of the Earth's surface, and a point somewhere in the air above it. The atmosphere in different regions is often found to be at different local potentials, which differ from that of the earth sometimes even by as much as 3000 volts within Vorlage:Convert. The upper stratum is positively charged, while the Earth's surface is itself negatively charged; the stratum of denser air between acting like the dielectric of a capacitor in keeping the opposite charges separate.

Atmospheric electricity can affect electrical communications. During storms, communication may be disrupted, and electrical discharges may be seen between sharp points on signalling equipment that is inadequately earthed. In old telegraph systems, the electromagnets could be physically damaged and the wiring was known to melt. More rarely, persistent stray currents can cause more subtle effects.

Electric currents created in sunward ionosphere.

Variations

Global daily cycles in the atmospheric electric field, with a minimum around 03 UT and peaking roughly 16 hours later, were researched by the Carnegie Institution of Washington in the 20th century. This Carnegie curve variation has been described as "the fundamental electrical heartbeat of the planet".

Even away from thunderstorms, atmospheric electricity can be highly variable, but, generally, the electric field is enhanced in fogs and dust whereas the atmospheric electrical conductivity is diminished.

Near space

At elevations above the clouds, atmospheric electricity forms a continuous and distinct element (called the electrosphere) in which the Earth is surrounded. The electrosphere layer (from tens of kilometers above the surface of the earth to the ionosphere) has a high electrical conductivity and is essentially at a constant electric potential. The ionosphere is the inner edge of the magnetosphere and is the part of the atmosphere that is ionized by solar radiation. (Photoionisation is a physical process in which a photon is incident on an atom, ion or molecule, resulting in the ejection of one or more electrons.)

Cosmic radiation

See also: Cosmic rays in ambient radiation and Orders of magnitude (radiation)

The Earth, and all living things on it, are constantly bombarded by radiation from outer space. This radiation primarily consists of positively charged ions from protons to iron and larger nuclei derived sources outside our solar system. This radiation interacts with atoms in the atmosphere to create an air shower of secondary ionising radiation, including X-rays, muons, protons, alpha particles, pions, and electrons. Ionisation from this secondary radiation ensures that the atmosphere is weakly conductive, and that the slight current flow from these ions over the Earth's surface balances the current flow from thunderstorms.

Aurora Borealis as seen over Canada at 11,000m (36,000 ft)

Earth-Ionosphere cavity

Vorlage:Main article The Potential difference between the ionosphere and the Earth is maintained by thunderstorms. In the Earth-ionosphere cavity, the electric field and conduction current in the lower atmosphere are primarily controlled by ions. Ions have characteristic parameters such as mobility, lifetime, and generation rate that vary with altitude.

The Schumann resonance is a set of spectrum peaks in the extremely low frequency (ELF) portion of the Earth's electromagnetic field spectrum. Schumann resonance is due to the space between the surface of the Earth and the conductive ionosphere acting as a waveguide. The limited dimensions of the earth cause this waveguide to act as a resonant cavity for electromagnetic waves. The cavity is naturally excited by energy from lightning strikes.

Thunderstorms and lightning

World map showing frequency of lightning strikes, in flashes per km² per year (equal-area projection). Lightning strikes most frequently in the Democratic Republic of the Congo. Combined 1995–2003 data from the Optical Transient Detector and 1998–2003 data from the Lightning Imaging Sensor.

If the quantity of water that is condensed in and subsequently precipitated from a cloud is known, then the total energy of a thunderstorm can be calculated. In an average thunderstorm, the energy released amounts to about 10,000,000 kilowatt-hours (3.6Vorlage:E joule), which is equivalent to a 20-kiloton nuclear warhead. A large, severe thunderstorm might be 10 to 100 times more energetic.

How lightning initially forms is still a matter of debate: Scientists have studied root causes ranging from atmospheric perturbations (wind, humidity, and atmospheric pressure) to the impact of solar wind and accumulation of charged solar particles. Ice inside a cloud is thought to be a key element in lightning development, and may cause a forcible separation of positive and negative charges within the cloud, thus assisting in the formation of lightning.

An average bolt of lightning carries a negative electric current of 40 kiloamperes (kA) (although some bolts can be up to 120 kA), and transfers a charge of five coulombs and energy of 500 MJ, or enough energy to power a 100-watt lightbulb for just under two months. The voltage depends on the length of the bolt, with the dielectric breakdown of air being three million volts per meter, and lightning bolts often being several hundred meters long. However, lightning leader development is not a simple matter of dielectric breakdown, and the ambient electric fields required for lightning leader propagation can be a few orders of magnitude less than dielectric breakdown strength. Further, the potential gradient inside a well-developed return-stroke channel is on the order of hundreds of volts per meter or less due to intense channel ionization, resulting in a true power output on the order of megawatts per meter for a vigorous return-stroke current of 100 kA .

Lightning sequence (Duration: 0.32 seconds)

Electrification in the air

A depiction of atmospheric electricity in a Martian dust storm, which has been suggested as a possible explanation for enigmatic chemistry results from Mars. (see also Viking lander biological experiments)

St. Elmo's Fire is an electrical phenomenon in which luminous plasma is created by a coronal discharge originating from a grounded object. Ball lightning is often erroneously identified as St. Elmo's Fire. They are separate and distinct phenomena. Although referred to as "fire", St. Elmo's Fire is, in fact, plasma, and is observed, usually during a thunderstorm, at the tops of trees, spires or other tall objects, or on the heads of animals, as a brush or star of light.

Corona is caused by the electric field around the object in question ionizing the air molecules, producing a faint glow easily visible in low-light conditions. Approximately 1,000 – 30,000 volts per centimetre is required to induce St. Elmo's Fire; however, this number is dependent on the geometry of the object in question. Sharp points tend to require lower voltage levels to produce the same result because electric fields are more concentrated in areas of high curvature, thus discharges are more intense at the end of pointed objects. St. Elmo's Fire and normal sparks both can appear when high electrical voltage affects a gas. St. Elmo's fire is seen during thunderstorms when the ground below the storm is electrically charged, and there is high voltage in the air between the cloud and the ground. The voltage tears apart the air molecules and the gas begins to glow. The nitrogen and oxygen in the Earth's atmosphere causes St. Elmo's Fire to fluoresce with blue or violet light; this is similar to the mechanism that causes neon signs to glow.

Electrical system grounding

Vorlage:Main article Atmospheric charges can cause undesirable, dangerous, and potentially lethal charge potential buildup in suspended electric wire power distribution systems. Bare wires suspended in the air spanning many kilometers and isolated from the ground can collect very large stored capacitance at high voltage static charge potentials, even when there is no thunderstorm or lightning occurring. This charge potential will seek to discharge itself through the path of least insulation, which can occur when a person reaches out to activate a power switch or to use an electric device.

To dissipate atmospheric charge buildup, one side of the electrical distribution system is connected to the earth at many points throughout the distribution system, as often as on every support pole. The one earth-connected wire is commonly referred to as the "protective earth", and provides path for the charge potential to dissipate without causing damage, and provides redundancy in case any one of the ground paths is poor due to corrosion or poor ground conductivity. The additional electric grounding wire that carries no power serves a secondary role, providing a high-current short-circuit path to rapidly blow fuses and render a damaged device safe, rather than have an ungrounded device with damaged insulation become "electrically live" via the grid power supply, and hazardous to touch.

Each transformer in an alternating current distribution grid segments the grounding system into a new separate circuit loop. These separate grids must also be grounded on one side to prevent charge buildup within them relative to the rest of the system, and which could cause damage from charge potentials discharging across the transformer coils to the other grounded side of the distribution network.

See also

General

Geophysics, Atmospheric sciences, Atmospheric physics, Atmospheric dynamics, Journal of Geophysical Research, Earth system model, Atmospheric chemistry, Ionosphere, Air quality, Lightning rocket

Electromagnetism

Earth's magnetic field, Sprites and lightning, Whistler (radio), Telluric currents, relaxation time, electrode effect, potential gradient

Other

Charles Chree Medal, Electrodynamic tethers, Solar radiation

People

Egon Schweidler, Charles Chree, Nikola Tesla, Hermann Plauson, Joseph Dwyer

References and external articles

General references

Pre-1930s

• Transcript of hand-written article signed by Dr. Mahlon Loomis, January 7, 1872. (from Radio News, November, 1922, pages 974–978 (Loomis lecture extract))
• "Atmospheric electricityVorlage:Toter Link/!...nourl (Seite dauerhaft nicht mehr abrufbar, festgestellt im Oktober 2016.)", dge.inpe.br.
• Chree, Charles, "Atmospheric electricity", Britannica Encyclopedia. Encyclopædia Britannica, 1926.
• "Chauncy J. Britten's Atmospheric Electrical Generator", Rex Research.
• Arthur William Poyser, Magnetism and Electricity. Longmans, Green and Co. 1901.
• Jeremiah Joyce, Scientific dialogues, with corrections by O. Gregory. Darton 1846.
• Dionysius Lardner, Popular Lectures on Science and Art, Atmospheric electricity. Henry W. Law 1856.
• Mr Wilson, On a Portable Gold-leaf Electrometer, etc.. Proceedings of the Cambridge Philosophical Society
• Alfred Urbanitzky, Electricity in the Service of Man. Atmospheric electricity. Cassell & Company, Limited 1886.
• Willis Isbister Milham, Meteorology, Atmospheric electricity. The Macmillan Company 1912.
• William Allen Miller, Elements of Chemistry: Theoretical and Practical, Atmospheric electricity.
• Jacques Wardlaw Redway, Handbook of Meteorology: A Manual for Cooperative Observers and Students, Atmospheric electricity.. John Wiley & Sons, inc. 1921.
• Experiments on Atmospheric Electricity. By Dr. L. Weber. Elektrotechnische Zeitschrift, 1889, p. 521.
• Francis Rolt-Wheeler, The Science-history of the Universe, Electrostatics – Atmospheric electricity. The Current Literature Publishing Company 1909.
• Golding Bird, Elements of Natural Philosophy, Atmospheric electricity. Lea and Blanchard 1848.
• George Carey Foster, Alfred William Porter, Jules François Joubert, Elementary Treatise on Electricity and Magnetism, Atmospheric electricity. Longmans, 1909.
• John Brocklesby Elements of Meteorology, Atmospheric electricity. Sheldon and company 1869.
• Terrestrial electricity, Year Book – Carnegie Institution of Washington.
• Frank Hagar Bigelow, A Treatise on the Sun's Radiation and Other Solar Phenomena, Atmospheric Electricity and the Diurnal Convection. John Wiley & Sons, Inc. 1918.
• Louis Agricola Bauer, John Adam Fleming, Terrestrial Magnetism and Atmospheric Electricity. University of Cincinnati 1919.
• David Ames Wells, Wells's Natural Philosophy, Atmospheric electricity. Ivison, Blakeman, Taylor & co. 1876.
• Karl Friedrich Peschel, Ebenezer West (Tr.), Elements of Physics, Atmospheric electricity and the electrical phenomena of life. Longman, Brown, Green, and Longmans 1846.

Journals

Articles

• F. J. Anderson, G. D. Freier: Interactions of the thunderstorm with a conducting atmosphere. In: J. Geophys. Res. 74. Jahrgang, Nr. 5390–5396, S. 1969. 
• Brook, M., "Thunderstorm electrification", Problems of Atmospheric and Space Electricity. S. C. Coroniti (Ed.), Elsevier, Amsterdam, pp. 280–283, 1965.
• W. M. Farrell, T. L. Aggson, E. B. Rodgers, W. B. Hanson: Observations of ionospheric electric fields above atmospheric weather systems. In: J. Geophys. Res. 99. Jahrgang, 1994, S. 19475–19484, doi:10.1029/94ja01135, bibcode:1994JGR....9919475F. 
• R. F. Fernsler, H. L. Rowland: Models of lightning-produced sprites and elves. In: J. Geophys. Res. 101. Jahrgang, 1996, S. 29653–29662, doi:10.1029/96jd02159, bibcode:1996JGR...10129653F. 
• A. C. Fraser-Smith: ULF magnetic fields generated by electrical storms and their significance to geomagnetic pulsation generation. In: Geophys. Res. Lett. 20. Jahrgang, Nr. 467–470, S. 1993. 
• Krider, E. P., and R. J. Blakeslee, "The electric currents produced by thunderclouds". J. Electrostatics, 16, 369–378, 1985.
• Lazebnyy, B. V., A. P. Nikolayenko, V. A. Rafal'skiy, and A. V. Shvets, "Detection of transverse resonances of the Earth-ionosphere cavity in the average spectrum of VLF atmospherics". Geomagn. Aeron., 28, 281–282, 1988.
• T Ogawa: Fair-weather electricity. In: J. Geophys. Res. 90. Jahrgang, Nr. 5951–5960, S. 1985. 
• D. D. Sentman: Schumann resonance spectra in a two-scale-height Earth-ionosphere cavity. In: J. Geophys. Res. 101. Jahrgang, Nr. 9479–9487, S. 1996. 
• L Wåhlin: Elements of fair weather electricity. In: J. Geophys. Res. 99. Jahrgang, 1994, S. 10767–10772, doi:10.1029/93jd03516, bibcode:1994JGR....9910767W. 

Other readings

• Richard E. Orville (ed.), "Atmospheric and Space Electricity". ("Editor's Choice" virtual journal) – "American Geophysical Union". (AGU) Washington, DC 20009-1277 USA
• Schonland, B. F. J., "Atmospheric Electricity". Methuen and Co., Ltd., London, 1932.
• MacGorman, Donald R., W. David Rust, D. R. Macgorman, and W. D. Rust, "The Electrical Nature of Storms". Oxford University Press, March 1998. ISBN 0-19-507337-1
• Cowling, Thomas Gilbert, "On Alfven's theory of magnetic storms and of the aurora", Terrestrial Magnetism and Atmospheric Electricity, 47, 209–214, 1942.
• H. H. Hoffert, "Intermittent Lightning-Flashes". Proc. Phys. Soc. London 10 No 1 (June 1888) 176–180.
• Volland, H., "Atmospheric Electrodynamics", Springer, Berlin, 1984.

Websites

• Bateman, Monte, "Atmospheric Electricity Homepage".
• "International Commission on Atmospheric Electricity". Commission of the International Association of Meteorology And Atmospheric Physics.
• "Lightning and Atmospheric Electricity". Global Hydrology and Climate Center, NASA.
• Kieft, Sandy, "The Langmuir Laboratory for Atmospheric Research". New Mexico Institute of Mining & Technology.
• "Power from the Air". Science and invention (Formerly Electrical Experimenter), Feb. 1922, no. 10. Vol IX, Whole No. 106. New York. (nuenergy.org)
• "Power from the Air". Science and invention (Formerly Electrical Experimenter), March 1922. (nuenergy.org).
• "RF Energy via Ionosphere". RF Energy Concepts Sec. 101 Rev. Nov., 2003
• Peter Winkler, "Early observations of and knowledge on air electricity and magnetism at Hohenpeißenberg during the Palatina". German Weather Service, Meteorological Observatory. (PDF)
• "Atmospheric Electricity". Meridian International Research.
• "Atmospheric Electricity and Plants"
• Do cosmic rays cause lightning? Ask the Experts – sciam.com January 24, 2008
• "The Earth's Electrical Environment". CPSMA, USA National Academies Press.

Further reading

• Auguste de La Rive, Explanation of the Diurnal Variations of the Magnetic Needle, and of theAurora Borealis (1894)
• James R. Wait, Some basic electromagnetic aspects of ULF field variations in the atmosphere. Journal Pure and Applied Geophysics, Volume 114, Number 1 / January, 1976 Pages 15–28 Birkhäuser Basel ISSN 0033-4553 (Print) 1420-9136 (Online) DOI 10.1007/BF00875488
• Charles Chree, Observations on Atmospheric Electricity at the Kew Observatory. Proceedings of the Royal Society of London, Vol. 60, 1896–1897 (1896–1897), pp. 96–132
• G. C. Simpson, C. S. Wrigh, Atmospheric Electricity over the Ocean. Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, Vol. 85, No. 577 (May 10, 1911), pp. 175–199
• National Research Council (U.S.)., & American Geophysical Union. (1986). The Earth's electrical environment. Washington, D.C: National Academy Pres
• Solar Dynamics and Its Effects on the Heliosphere and Earth By D. N. Baker, International Space Science Institute
• Solar variability, weather, and climate By National Research Council (U.S.). Geophysics Study Committee
• Philosophical magazine. (1839) London: Taylor & Francis. Instruction for the scientific expedition to the arctic region, Electrometers. pg 219.

External links

• Electric Current through the Atmosphere
• The Global Circuit, phys.uh.edu
• Soaking in atmospheric electricity 'Fair weather' measurements important to understanding thunderstorms. science.nasa.gov
• Atmospheric Electricity HomePage, uah.edu
• Tjt, Fair-weather atmospheric electricity. ava.fmi.fi
• ICAE – International Commission on Atmospheric Electricity Homepage