Schumann resonances
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The '''Schumann resonances (SR)''' are a set of spectrum peaks in the [[extremely low frequency]] (ELF) portion of the [[Earth]]'s [[electromagnetic field]] spectrum. Schumann resonances are global electromagnetic [[resonance]]s, excited by [[lightning]] discharges in the cavity formed by the [[Earth]] surface and the [[ionosphere]].
==Description==
This global electromagnetic [[resonance]] phenomenon is named after physicist [[Winfried Otto Schumann]] who predicted it mathematically in 1952. Schumann resonance occurs because the space between the surface of the [[Earth]] and the conductive [[ionosphere]] acts as a [[waveguide]]. The limited dimensions of the [[Earth]] cause this [[waveguide]] to act as a [[resonant cavity]] for [[electromagnetic waves]] in the [[extremely low frequency|ELF]] band. The cavity is naturally excited by energy from [[lightning]] strikes. Schumann resonance modes are observed in the power spectra of the natural electromagnetic background noise, as separate peaks at extremely low frequencies (ELF) around 7.8, 14.3, 20.8, 27.3 and 33.8 Hz.
The [[Fundamental frequency|fundamental mode]] of the Schumann resonance is a [[standing wave]] in the Earth-ionosphere cavity with a [[wavelength]] equal to the [[circumference]] of the [[Earth]]. This lowest-frequency (and highest-intensity) mode of the Schumann [[resonance]] occurs at a [[frequency]] of approximately 7.8 Hz. Further resonance modes appear at approximately 6.5 Hz intervals, a characteristic attributed to the atmosphere's spherical geometry. The peaks exhibit a spectral width of approximately 20% on account of the damping of the respective modes in the dissipative cavity. The eighth [[overtone]] lies at approximately 59.9 Hz.
Schumann resonances are used to track global [[lightning]] activity. Owing to the connection between [[lightning]] activity and the Earth's [[climate]] they can also be used to monitor global temperature variations and variations of upper water vapor. Extraterrestrial lightning may also be detected and studied with Schumann resonances. Schumann resonances have been used for research and monitoring of the lower [[ionosphere]] on [[Earth]] and was suggested for exploration of lower [[ionosphere]] parameters on [[celestial]] bodies. Schumann resonances can be used to track geomagnetic and ionospheric disturbances. More recently, Schumann resonances have been used for monitoring transient luminous events – [[upper-atmospheric lightning#Sprites|sprites]], [[upper-atmospheric lightning#Elves|elves]], [[upper-atmospheric lightning#Blue jets|jets]], and other [[upper-atmospheric lightning]]. A new field of interest using Schumann resonances is related to short-term [[earthquake prediction]]. Schumann resonances have gone beyond the boundaries of [[physics]], invading [[medicine]], raising interest in artists and musicians, and gaining interest from fringe fields such as [[psychobiology]].
==History==
The first suggestion that an [[ionosphere]] existed, capable of trapping [[electromagnetic waves]], was made by [[Heaviside]] and Kennelly in 1902 <ref name=" Heaviside">{{cite journal | author=O. Heaviside | title= Telegraphy, Sect. 1, Theory | journal= Encyc. Brit.10th ed.. . London | volume=9 |year=1902 | pages=213–218}}</ref> <ref name=" Kennelly ">{{cite journal | author=A.E. Kennelly | title= On the elevation of the electrically-conducting strata of the earth's atmosphere | journal= Electrical world and engineer | volume=32 |year=1902 | pages=473–473}}</ref>. It took another twenty years before [[Edward Appleton]] and Barnett in 1925 <ref name=" Appleton ">{{cite journal | author= Appleton, E. V. , M. A. F. Barnett | title= On Some Direct Evidence for Downward Atmospheric Reflection of Electric Rays | journal= Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | volume=109(752) |year=1925 | pages=621–641 | doi= 10.1098/rspa.1925.0149}}</ref>, were able to prove experimentally the existence of the [[ionosphere]]. However, even prior to this, the first documented observations of global electromagnetic resonances were made by [[Nikola Tesla]] in 1905 and formed the basis for his scheme for [[wireless energy transmission]] <ref name=" Tesla ">{{cite journal | author= N. Tesla | title= The Transmission of Electrical Energy Without Wires As A Means Of Furthering World Peace | journal= Electrical World And Engineer | volume= January 7 |year=1905 | pages=21–24}}</ref>. Although some of the most important mathematical tools for dealing with spherical [[waveguide]]s were developed by Watson in 1918 <ref name="Watson">{{cite journal | author= Watson, G.N. | title= The diffraction of electric waves by the Earth | journal= Proc. Roy. Soc. (London) | volume= Ser.A 95 |year=1918| pages=83–99}}</ref>, it was [[Winfried Otto Schumann]] who first studied the theoretical aspects of the global [[resonance]]s of the earth-ionosphere [[waveguide]] system, known today as the Schumann resonances. In 1952-1954 Schumann, together with Köning, attempted to measure the resonant frequencies <ref name=" Schumann a">{{cite journal | author= Schumann W. O. | title= Über die strahlungslosen Eigenschwingungen einer leitenden Kugel, die von einer Luftschicht und einer Ionosphärenhülle umgeben ist | journal= Zeitschrift und Naturfirschung | volume= 7a |year=1952| pages=149–154}}</ref> <ref name=" Schumann b">{{cite journal | author= Schumann W. O. | title= Über die Dämpfung der elektromagnetischen Eigenschwingnugen des Systems Erde – Luft – Ionosphäre | journal= Zeitschrift und Naturfirschung | volume= 7a |year=1952| pages=250–252}}</ref> <ref name=" Schumann c">{{cite journal | author= Schumann W. O. | title= Über die Ausbreitung sehr Langer elektriseher Wellen um die Signale des Blitzes | journal= Nuovo Cimento | volume= 9 |year=1952| pages=1116–1138 | doi= 10.1007/BF02782924}}</ref> <ref name=" Schumann d">{{cite journal | author= Schumann W. O. and H. König | title= Über die Beobactung von Atmospherics bei geringsten Frequenzen | journal= Naturwiss | volume= 41 |year=1954| pages=183–184 | doi= 10.1007/BF00638174}}</ref> . However, it was not until measurements made by Balser and Wagner in 1960-1963 <ref name=" Balser Wagner a">{{cite journal | author= Balser M. and C. Wagner | title= Measurement of the spectrum of radio noise from 50 to 100 c/s | journal= J.Res. NBS | volume= 64D |year=1960 | pages=415–418}}</ref> <ref name=" Balser Wagner b">{{cite journal | author= Balser M. and C. Wagner | title= Observations of earth-ionosphere cavity resonances | journal= Nature | volume= 188 |year=1960 | pages=638–641 | doi= 10.1038/188638a0}}</ref> <ref name=" Balser Wagner c">{{cite journal | author= Balser M. and C. Wagner | title= Diurnal power variations of the earth-ionosphere cavity modes and their relationship to worldwide thunderstorm activity | journal= J.G.R | volume= 67 |year=1962 | pages=619–625 | doi= 10.1029/JZ067i002p00619}}</ref> <ref name=" Balser Wagner d">{{cite journal | author= Balser M. and C. Wagner | title= On frequency variations of the earth-ionosphere cavity modes | journal= J.G.R | volume= 67 |year=1962 | pages=4081–4083 | doi= 10.1029/JZ067i010p04081}}</ref> <ref name=" Balser Wagner e">{{cite journal | author= Balser M. and C. Wagner | title= Effect of a high-altitude nuclear detonation on the earth-ionosphere cavity | journal= J.G.R | volume= 68 |year=1963 | pages=4115–4118}}</ref> that adequate analysis techniques were available to extract the [[resonance]] information from the background noise. Since then there has been an increasing interest in Schumann resonances in a wide variety of fields.
==Basic theory==
Lightning discharges are considered as the primary natural source of Schumann resonances. Lightning channels behave like a huge antenna which radiates [[electromagnetic energy]] as impulsive signals at frequencies below about 100 kHz <ref name=" Volland ">{{cite book | author= Volland, H. | title= Atmospheric Electrodynamics | publisher = Springer-Verlag, Berlin | year=1984}}</ref>. These signals are very weak, but the earth-ionosphere [[waveguide]] behaves like a [[resonator]] at ELF frequencies and amplifies the spectral signals from [[lightning]] at the [[resonance]] frequencies <ref name=" Volland ">{{cite book | author= Volland, H. | title= Atmospheric Electrodynamics | publisher = Springer-Verlag, Berlin | year=1984}}</ref>.
In an ideal cavity, the [[resonant frequency]] of the <math>n</math>-th mode <math>f_{n}</math> is determined by the [[Earth radius]] <math>a</math> and the [[speed of light]] <math>c</math> <ref name=" Schumann a">{{cite journal | author= Schumann W. O. | title= Über die strahlungslosen Eigenschwingungen einer leitenden Kugel, die von einer Luftschicht und einer Ionosphärenhülle umgeben ist | journal= Zeitschrift und Naturfirschung | volume= 7a |year=1952| pages=149–154}}</ref>.
:<math>f_{n} =\frac{c}{2 \pi a}\sqrt{n(n+1)}</math>
The real Earth-ionosphere [[waveguide]] is not a perfect electromagnetic cavity. Losses due to finite [[ionosphere]] [[electrical conductivity]] make the system resonate at lower frequencies than would be expected in an ideal case, and the observed peaks are wide. In addition there are a number of horizontal asymmetries – day-night transition, latitudinal changes in the [[Earth magnetic field]], sudden ionospheric disturbances, polar cap absorption, etc. that complicate the Schumann resonance power spectra.
==Measurements==
Today Schumann resonances are recorded by many stations around the world. The electromagnetic sensors used to measure Schumann resonances consist of two horizontal antennas for receiving the [[magnetic field]] in the north-south and the east-west direction and one vertical antenna for observing the vertical [[electric field]]. Since Schumann resonance frequencies are extremely low, practical antennas would have to be hundreds of kilometers long. In addition, the Schumann resonance electric field amplitude (~300 microVolts/m) is much smaller than the static electric field (~150 V/m) in the [[atmosphere]]. Similarly, the amplitude of the Schumann resonance magnetic field (~1 picoTesla) is [[orders of magnitude]] smaller than the [[Earth magnetic field]] (~30-50 microTesla) <ref name="Price et al.">{{cite journal | author= Price, C., O. Pechony, E. Greenberg | title= Schumann resonances in lightning research | journal= Journal of Lightning Research | volume= 1 |year=2006| pages=1– 15}}</ref> . Therefore, special receivers and antennas are needed to measure Schumann resonances. The electric component is commonly measured with a ball antenna, suggested by Ogawa et al. in 1966 <ref name="Ogawa">{{cite journal | author= Ogawa, T., Y. Tanka, T. Miura, and M. Yasuhara | title= Observations of natural ELF electromagnetic noises by using the ball antennas | journal= J. Geomagn. Geoelectr | volume= 18 |year=1966| pages=443– 454}}</ref> , connected to a high-impedance [[amplifier]]. The [[magnetic field]] is measured with magnetic [[induction coil]]s consisting of tens of thousands of turns around material with very high [[magnetic permeability]].
==Applications==
===Global lightning activity ===
From the very beginning of Schumann resonance studies, they were used to monitor global [[lightning]] activity by tracking changes in Schumann resonance field intensities. At any given time there are about 2000 [[thunderstorms]] around the [[globe]] <ref name=" Heckman ">{{cite journal | author= Heckman S. J., E. Williams, | title= Total global lightning inferred from Schumann resonance measurements | journal= J. G. R. | volume= 103(D24) |year=1998| pages=31775–31779 | doi= 10.1029/98JD02648}}</ref>. Producing ~50 [[lightning]] events per [[second]] <ref name="Christian ">{{cite journal | author= Christian H. J., R.J. Blakeslee, D.J. Boccippio, W.L. Boeck, D.E. Buechler, K.T. Driscoll, S.J. Goodman, J.M. Hall, W.J. Koshak, D.M. Mach, M.F. Stewart, | title= Global frequency and distribution of lightning as observed from space by the Optical Transient Detector | journal= J. G. R. | volume= 108(D1) |year=2003| pages=4005 | doi= 10.1029/2002JD002347}}</ref>, these [[thunderstorms]] create the background Schumann resonance signal.
Determining the spatial [[lightning]] distribution from Schumann resonance records is a complex problem: in order to properly estimate the [[lightning]] intensity from Schumann resonance records it is necessary to account for both the distance to [[lightning]] sources as well as the wave propagation between the source and the observer. The common approach is to make a preliminary assumption on the spatial [[lightning]] distribution, basing on the known properties of [[lightning]] [[climatology]]. An alternative approach is placing the receiver at the North or South Pole, which remain approximately [[equidistant]] from the main thunderstorm centers during the day <ref name=" Nickolaenko 97">{{cite journal | author= Nickolaenko, A.P. | title= Modern aspects of Schumann resonance studies | journal= J.A.S.T.P. | volume= 59 |year=1997| pages=806–816}}</ref>. One method not requiring preliminary assumptions on the [[lightning]] distribution <ref name=" Shvets">{{cite journal | author= Shvets A.V. | title= A technique for reconstruction of global lightning distance profile from background Schumann resonance signal | journal= J.A.S.T.P. | volume= 63 |year=2001| pages=1061–1074}}</ref> is based on the decomposition of the average background Schumann resonance spectra, utilizing ratios between the average electric and magnetic spectra and between their linear combinations.
====Diurnal variations ====
The best documented and the most debated features of the Schumann resonance phenomenon are the diurnal variations of the background Schumann resonance power spectrum.
A characteristic Schumann resonance diurnal record reflects the properties of both global [[lightning]] activity and the state of the earth-ionosphere cavity between the source region and the observer. The vertical [[electric field]], which is equally sensitive in all directions and therefore measures the global [[lightning]], shows three dominant maxima, associated with the three “hot spots” of planetary [[lightning]] activity: 9 UT ([[Universal Time]]) peak, linked to the increased [[thunderstorm]] activity from south-east Asia; 14 UT peak associated with the peak in African [[lightning]] activity; and the 20 UT peak resulting for the increase in [[lightning]] activity in South America. The time and [[amplitude]] of the peaks vary throughout the year, reflecting the seasonal changes in [[lightning]] activity.
=====”Chimney” ranking =====
In general, the African peak is the strongest, reflecting the major contribution of the African “chimney” to the global [[lightning]] activity. The ranking of the two other peaks – Asian and American – is the subject of a vigorous dispute among Schumann resonance scientists. Experimental Schumann resonance data show a greater contribution from Asia than from South America. This contradicts optical satellite and climatological [[lightning]] data that show the South American thunderstorm center stronger than the Asian center <ref name="Christian ">{{cite journal | author= Christian H. J., R.J. Blakeslee, D.J. Boccippio, W.L. Boeck, D.E. Buechler, K.T. Driscoll, S.J. Goodman, J.M. Hall, W.J. Koshak, D.M. Mach, M.F. Stewart, | title= Global frequency and distribution of lightning as observed from space by the Optical Transient Detector | journal= J. G. R. | volume= 108(D1) |year=2003| pages=4005 | doi= 10.1029/2002JD002347}}</ref>. The reason for such disparity remains unclear. Williams and Sátori <ref name="Williams Satori">{{cite journal | author= Williams E. R., G. Sátori | title= Lightning, thermodynamic and hydrological comparison of the two tropical continental chimneys | journal= J.A.S.T.P. | volume= 66 |year=2004| pages=1213–1231}}</ref> suggest that in order to obtain “correct” Asia-America chimney ranking, it is necessary to remove the influence of the day/night variations in the ionospheric conductivity (day-night asymmetry influence) from the Schumann resonance records. On the other hand, such “corrected” records presented in the work by Sátori et al. <ref name="Satori ">{{cite journal | author= Sátori G., M. Neska, E. Williams, J. Szendrői | title= Signatures of the non-uniform Earth-ionosphere cavity in high time-resolution Schumann resonance records | journal= Radio Science | volume= in print |year=2007 }}</ref> show that even after the removal of the day-night asymmetry influence from Schumann resonance records, the Asian contribution remains greater than American. Similar results were obtained by Pechony et al. <ref name="Pechony et al">{{cite journal | author= Pechony, O., C. Price, A.P. Nickolaenko | title= Relative importance of the day-night asymmetry in Schumann resonance amplitude records | journal= Radio Science | volume= in print |year=2007 }}</ref> who calculated Schumann resonance fields from satellite [[lightning]] data. Both simulations – those neglecting the day-night asymmetry, and those taking this asymmetry into account, showed same Asia-America chimney ranking. As for today, the reason for the “invert” ranking of Asia and America chimneys in Schumann resonance records remains unclear and the subject requires further, targeted research.
=====Influence of the day-night asymmetry =====
In the early literature the observed diurnal variations of Schumann resonance power were explained by the variations in the source-receiver (lightning-observer) geometry <ref name=" Balser Wagner a">{{cite journal | author= Balser M. and C. Wagner | title= Measurement of the spectrum of radio noise from 50 to 100 c/s | journal= J.Res. NBS | volume= 64D |year=1960 | pages=415–418}}</ref>. It was concluded that no particular systematic variations of the [[ionosphere]] (which serves as the upper [[waveguide]] boundary) are needed to explain these variations <ref name=" Madden ">{{cite journal | author= Madden T., W. Thompson | title= Low-frequency electromagnetic oscillations of the Earth-ionosphere cavity | journal= Rev. Geophys. | volume= 3(2) |year=1965| pages=211 | doi= 10.1029/RG003i002p00211}}</ref>. Subsequent theoretical studies supported the early estimations of the small influence of the [[ionosphere]] day-night asymmetry (difference between day-side and night-side [[ionosphere]] conductivity) on the observed variations in Schumann resonance field intensities <ref name=" Nick 2002 ">{{cite book | author= Nickolaenko A. P. and M. Hayakawa | title Resonances in the Earth-ionosphere cavity | publisher = Kluwer Academic Publishers, Dordrecht-Boston-London | year=2002}}</ref>.
The interest in the influence of the day-night asymmetry in the [[ionosphere]] conductivity on Schumann resonances gained a new strength in the 1990s, after publication of a work by Sentman and Fraser <ref name=" Sentman Fraser ">{{cite journal | author= Sentman, D.D., B. J. Fraser | title=Simultaneous observations of Schumann Resonances in California and Australia - Evidence for intensity modulation by the local height of the D region | journal= Journal of geophysical research | volume=96(9) | year=1991 | pages=15973–15984 | doi=10.1029/91JA01085}}</ref>. Sentman and Fraser developed a technique to separate the global and the local contributions to the observed field power variations using records obtained [[simultaneously]] at two stations. Sentman and Fraser interpreted the local contribution as [[ionosphere]] height variation. Their work convinced many scientists in the importance of the ionospheric day-night asymmetry and inspired numerous experimental studies. However recently it was shown that results obtained by Sentman and Fraser can be approximately simulated with a uniform model (without taking into account [[ionosphere]] day-night variation) and therefore cannot be solely interpreted in terms of [[ionosphere]] height variation <ref name=" Pechony Price ">{{cite journal | author= Pechony, O., C. Price | title= Schumann Resonances: interpretation of local diurnal intensity modulations | journal= Radio Sci.| volume=41, 42(2) | year=2006 | doi= 10.1029/2006RS003455 | pages= RS2S05 | unused_data= |RS2S05, doi=10.1029/2006RS003455}}</ref> .
Schumann resonance [[amplitude]] records show significant diurnal and seasonal variations which in general coincide in time with the times of the day-night transition (the [[Terminator (solar)|terminator]]). This time-matching seems to support the suggestion of a significant influence of the day-night [[ionosphere]] asymmetry on Schumann resonance amplitudes. There are records showing almost clock-like accuracy of the diurnal amplitude changes <ref name="Satori ">{{cite journal | author= Sátori G., M. Neska, E. Williams, J. Szendrői | title= Signatures of the non-uniform Earth-ionosphere cavity in high time-resolution Schumann resonance records | journal= Radio Science | volume= in print |year=2007 }}</ref>. On the other hand there are numerous days when Schumann Resonance amplitudes do not increase at [[sunrise]] or do not decrease at [[sunset]]. There are studies showing that the general behavior of Schumann resonance [[amplitude]] records can be recreated from diurnal and seasonal [[thunderstorm]] migration, without invoking ionospheric variations <ref name=" Nick 2002 ">{{cite book | author= Nickolaenko A. P. and M. Hayakawa | title Resonances in the Earth-ionosphere cavity | publisher = Kluwer Academic Publishers, Dordrecht-Boston-London | year=2002}}</ref> <ref name="Pechony et al">{{cite journal | author= Pechony, O., C. Price, A.P. Nickolaenko | title= Relative importance of the day-night asymmetry in Schumann resonance amplitude records | journal= Radio Science | volume= in print |year=2007 }}</ref>. Two recent independent theoretical studies have shown that the variations in Schumann resonance power related to the day-night transition are much smaller than those associated with the peaks of the global [[lightning]] activity, and therefore the global [[lightning]] activity plays a more important role in the variation of the Schumann resonance power <ref name=" Yang Pasko ">{{cite journal | author= Yang H., V. P. Pasko | title= Three-dimensional finite difference time domain modeling of the diurnal and seasonal variations in Schumann resonance parameters | journal= Radio Science | volume= 41 | year=2007 | doi= 10.1029/2005RS003402 | pages= RS2S14 | unused_data= |RS2S14, doi=10.1029/2005RS003402}}</ref> <ref name="Pechony et al">{{cite journal | author= Pechony, O., C. Price, A.P. Nickolaenko | title= Relative importance of the day-night asymmetry in Schumann resonance amplitude records | journal= Radio Science | volume= in print |year=2007 }}</ref>.
It is generally acknowledged that source-observer effects are the dominant source of the observed diurnal variations, but there remains considerable controversy about the degree to which day-night signatures are present in the data. Successful monitoring of global thunderstorm activity with Schumann resonances relies on the proper interpretation of experimental data. It is therefore vital to understand and correctly interpret the major features of Schumann resonance field power variations.
==== The “inverse problem” ====
One of the interesting problems in Schumann resonances studies is determining the [[lightning]] source characteristics (the “inverse problem”). Temporally resolving each individual flash is impossible,{{Clarifyme|date=March 2008}} but there are intense ELF transient events, also named ‘‘Q bursts’’. Q-bursts are triggered by intense [[lightning]] strikes, associated with a large charge transfer and often high peak current <ref name="Ogawa">{{cite journal | author= Ogawa, T., Y. Tanka, T. Miura, and M. Yasuhara | title= Observations of natural ELF electromagnetic noises by using the ball antennas | journal= J. Geomagn. Geoelectr | volume= 18 |year=1966| pages=443– 454}}</ref>. Q-bursts can exceed the [[amplitude]] of the background signal level by a factor of 10 and appear with intervals of ~10sec <ref name=" Shvets">{{cite journal | author= Shvets A.V. | title= A technique for reconstruction of global lightning distance profile from background Schumann resonance signal | journal= J.A.S.T.P. | volume= 63 |year=2001| pages=1061–1074}}</ref>, which allows to consider them as isolated events and determine the source [[lightning]] location. The source location is determined with either multi-station or single-station techniques. The multi-station techniques are more accurate, but require more complicated and expensive facilities.
=== Transient luminous events research ===
It is now believed that many of the Schumann resonances transients (Q bursts) are related to the transient luminous events (TLEs). In 1995 Boccippio et al. <ref name=" Boccippio 95">{{cite journal | author= Boccippio, D. J., E. R. Williams, S. J. Heckman, W. A. Lyons, I. T. Baker, R. Boldi | title= Sprites, ELF transients, and positive ground strokes | journal= Science | volume= 269| year=1995 | pages=1088–1091 | doi= 10.1126/science.269.5227.1088 | pmid= 17755531}}</ref> suggested that sprites, the most common TLE, are produced by positive cloud-to-ground [[lightning]] occurring in the stratiform region of a [[thunderstorm]] system, and are accompanied by Q-burst in the Schumann resonances band. Recent observations <ref name=" Boccippio 95">{{cite journal | author= Boccippio, D. J., E. R. Williams, S. J. Heckman, W. A. Lyons, I. T. Baker, R. Boldi | title= Sprites, ELF transients, and positive ground strokes | journal= Science | volume= 269| year=1995 | pages=1088–1091 | doi= 10.1126/science.269.5227.1088 | pmid= 17755531}}</ref> <ref name=" Price et al 04">{{cite journal | author= Price, C., E. Greenberg, Y. Yair, G. Sátori, J. Bór, H. Fukunishi, M. Sato, P. Israelevich, M. Moalem, A. Devir, Z. Levin, J.H. Joseph, I. Mayo, B. Ziv, A. Sternlieb | title= Ground-based detection of TLE-producing intense lightning during the MEIDEX mission on board the Space Shuttle Columbia | journal= G.R.L. | volume= 31| year=2004 | unused_data= |L20107, doi=1029/2004GL020711}}</ref> reveal that occurrences of sprites and Q bursts are highly correlated and Schumann resonances data can possibly be used to estimate the global occurrence rate of sprites <ref name=" Hu ">{{cite journal | author= Hu, W., S. A. Cummer, W. A. Lyons, T. E. Nelson | title= Lightning charge moment changes for the initiation of sprites | journal= G.R.L. | volume= 29(8) | year=2002 | pages = 1279 | doi=10.1029/2001GL014593}}</ref>.
=== Climate change research ===
Global [[climate change]] is the subject of intense debate and concern. One of the important aspects in understanding [[global climate change]] is the development of tools and techniques that would allow continuous and long-term monitoring of processes affecting the [[global climate]]. Schumann resonances are one of the very few tools that can provide such global information reliably and cheaply.
==== Global temperature ====
Williams [1992] <ref name=" Williams 92">{{cite journal | author= Williams, E.R. | title= The Schumann resonance: a global tropical thermometer | journal= Science | volume= 256| year=1992| pages = 1184–1186 | doi= 10.1126/science.256.5060.1184 | pmid= 17795213}}</ref> suggested that global temperature may be monitored with the Schumann resonances. The link between Schumann resonance and temperature is [[lightning]] flash rate, which increases nonlinearly with temperature <ref name=" Williams 92">{{cite journal | author= Williams, E.R. | title= The Schumann resonance: a global tropical thermometer | journal= Science | volume= 256| year=1992| pages = 1184–1186 | doi= 10.1126/science.256.5060.1184 | pmid= 17795213}}</ref>. The [[nonlinearity]] of the [[lightning]]-to-temperature relation provides a natural [[amplifier]] of the temperature changes and makes Schumann resonance a sensitive “thermometer”. Moreover, the ice particles that are believed to participate in the electrification processes which result in a [[lightning]] discharge <ref name=" Williams 89">{{cite journal | author= Williams, E.R. | title= The tripole structure of thunderstorms | journal= J. G. R.| volume= 94| year=1989| pages = 13151–13167 | doi= 10.1029/JD094iD11p13151}}</ref> have an important role in the radiative feedback effects that influence the atmosphere temperature. Schumann resonances may therefore help us to understand these [[feedback]] effects.
==== Upper tropospheric water vapor ====
Tropospheric [[water vapor]] is a key element of the Earth’s climate, which has direct effects as a [[greenhouse gas]], as well as indirect effect through interaction with [[clouds]], [[aerosols]] and tropospheric chemistry. Upper tropospheric water vapor (UTWV) has a much greater impact on the [[greenhouse effect]] than [[water vapor]] in the lower [[atmosphere]] <ref name=" Hansen ">{{cite journal | author= Hansen, J., A. Lacis, D. Rind, G. Russel, P. Stone, I. Fung, R. Ruedy, J., Lerner | title= Climate sensitivity: Analysis of feedback mechanisms | journal= Climate Processes and Climate Sensitivity, J.,E. Hansen and T. Takahashi, eds.. AGU Geophys. Monograph | volume= 29 | year=1984| pages = 130–163}}</ref>, but whether this impact is a positive, or a negative [[feedback]] is still uncertain <ref name=" Rind ">{{cite journal | author= Rind, D. | title= Just add water vapor | journal= Science | volume= 28| year=1998| pages = 1152–1153 | doi= 10.1126/science.281.5380.1152}}</ref>. The main challenge in addressing this question is the difficulty in monitoring UTWV globally over long timescales. Continental deep-convective [[thunderstorms]] produce most of the [[lightning]] discharges on [[Earth]]. In addition, they transport large amount of [[water vapor]] into the upper [[troposphere]], dominating the variations of global UTWV. Price [2000] <ref name=" Price 00">{{cite journal | author= Price, C. | title= Evidence for a link between global lightning activity and upper tropospheric water vapor | journal= Letters to Nature | volume= 406 | year=2000 | pages = 290–293 | doi= 10.1038/35018543}}</ref> suggested that changes in the UTWV can be derived from records of Schumann Resonances.
=== Extraterrestrial lightning===
Existence of Schumann resonances is conditioned primarily by two factors: 1) presence of a substantial [[ionosphere]] with electric conductivity increasing with height from low values near the surface (or a high-conductivity layer, in case of gaseous planets); 2) source of excitation of [[electromagnetic waves]] in the ELF range. In [[Solar System]] there are five candidates for Schumann resonance detection: [[Venus]], [[Mars]], [[Jupiter]], [[Saturn]] and its moon [[Titan]].
Modeling Schumann resonances on the [[planets]] and [[moons]] of the [[Solar System]] is complicated by the lack of knowledge of the [[waveguide]] parameters, and today there is no possibility to validate the results. Nevertheless, theoretical results aid to estimate the possibility of detecting Schumann resonances on a [[planet]].
The strongest evidence for [[lightning]] on [[Venus]] comes from the impulsive [[electromagnetic waves]] detected by [[Venera]] 11 and 12 landers. Schumann resonances on [[Venus]] were studied by Nickolaenko and Rabinowicz [1982] <ref name=" Nickolaenko Venus">{{cite journal | author= Nickolaenko A. P., L. M. Rabinowicz | title= On the possibility of existence of global electromagnetic resonances on the planets of Solar system | journal= Space Res. | volume= 20 | year=1982| pages = 82–89}}</ref> and Pechony and Price [2004] <ref name=" Pechony Price 04">{{cite journal | author= Pechony, O., C. Price | title= Schumann resonance parameters calculated with a partially uniform knee model on Earth, Venus, Mars, and Titan | journal= Radio Sci.| volume= 39(5)| year=2004 | doi= 10.1029/2004RS003056 | pages= RS5007 | unused_data= |RS5007, doi=10.1029/2004RS003056}}</ref>. Both studies yielded very close results, indicating that Schumann resonances should be easily detectable on this [[planet]] given a suitably located sensor.
On [[Mars]] [[lightning]] activity has not been detected, but charge separation and [[lightning]] strokes are considered possible in the Martian dust storms <ref name=" Eden ">{{cite journal | author= Eden, H. F. and B. Vonnegut | title= Electrical breakdown caused by dust motion in low-pressure atmospheres: consideration for Mars | journal= Science | volume= 180 | year=1973| pages=962 | doi= 10.1126/science.180.4089.962 | pmid= 17735929}}</ref> <ref name=" Renno ">{{cite journal | author= Renno N. O., A. Wong, S. K. Atreya, I. de Pater, M. Roos-Serote | title= Electrical discharges and broadband radio emission by Martian dust devils and dust storms | journal= G. R. L.| volume= 30 (22)| year=2003| pages=2140 | doi= 10.1029/2003GL017879}}</ref> . Martian global resonances were modeled by Sukhorukov [1991] <ref name=" Sukhorukov ">{{cite journal | author= Sukhorukov A. I. | title= On the Schumann resonances on Mars | journal= Planet. Space Sci.| volume= 39(12) | year=1991| pages=1673–1676 | doi= 10.1016/0032-0633(91)90028-9}}</ref>, Pechony and Price [2004] <ref name=" Pechony Price 04">{{cite journal | author= Pechony, O., C. Price | title= Schumann resonance parameters calculated with a partially uniform knee model on Earth, Venus, Mars, and Titan | journal= Radio Sci.| volume= 39(5)| year=2004 | doi= 10.1029/2004RS003056 | pages= RS5007 | unused_data= |RS5007, doi=10.1029/2004RS003056}}</ref> and Molina-Cuberos et al. [2006] <ref name=" Molina-Cuberos ">{{cite journal | author= Molina-Cuberos G. J., J. A. Morente, B. P. Besser, J. Porti, H. Lichtenegger, K. Schwingenschuh, A. Salinas, J. Margineda | title= Schumann resonances as a tool to study the lower ionosphere of Mars | journal= Radio Science | volume= 41 | year=2006 | pages= RS1003 | doi= 10.1029/2004RS003187 | unused_data= |RS1003, doi=10.1029/2004RS003187}}</ref> . The results of the three studies are somewhat different, but it seems that at least the first two Schumann resonance modes should be detectable.
It was long ago suggested that [[lightning]] dischargers may occur on [[Titan]] <ref name=" Lammer ">{{cite journal | author= Lammer H., T. Tokano, G. Fischer, W. Stumptner, G. J. Molina-Cuberos, K. Schwingenschuh, H. O. Rucher | title= Lightning activity of Titan: can Cassiny/Huygens detect it?| journal= Planet. Space Sci. | volume= 49 | year=2001| pages=561–574 | doi= 10.1016/S0032-0633(00)00171-9}}</ref> , but recent data from [[Cassini-Huygens]] seems to indicate that there is no [[lightning]] activity on this largest [[satellite]] of [[Saturn]]. Due to the recent interest in [[Titan]], associated with the [[Cassini-Huygens]] mission, its [[ionosphere]] is perhaps the most thoroughly modeled today. Schumann resonances on [[Titan]] received more attention than on other [[celestial]] bodies. Schumann resonances on [[Titan]] were studied by Besser et al. [2002] <ref name=" Besser ">{{cite journal | author= Besser, B. P., K. Schwingenschuh, I. Jernej, H. U. Eichelberger, H. I. M. Lichtenegger, M. Fulchignoni, G. J. Molina-Cuberos, J. A. Morente, J. A. Porti, A.Salinas | title= Schumann resonances as indicators for lighting on Titan | journal= Proceedings of the Second European Workshop on Exo/Astrobiology, Graz, Australia, 16-19 Sep. | year=2002 }}</ref> , Morente et al. [2003] <ref name=" Morente ">{{cite journal | author= Morente J. A., Molina-Cuberos G. J., Porti J. A., K. Schwingenschuh, B. P. Besser | title= A study of the propagation of electromagnetic waves in Titan’s atmosphere with the TLM numerical method | journal= Icarus | volume= 162| year=2003| pages=374–384 | doi= 10.1016/S0019-1035(03)00025-3}}</ref> , Molina-Cuberos et al. [2004] <ref name=" Molina-Cuberos 04">{{cite journal | author= Molina-Cuberos G. J., J. Porti, B. P. Besser, J. A. Morente, J. Margineda, H. I. M. Lichtenegger, A. Salinas, K. Schwingenschuh, H. U. Eichelberger | title= Shumann resonances and electromagnetic transparence in the atmosphere of Titan | journal= Advances in Space Research | volume= 33 | year=2004| pages=2309–2313 | doi= 10.1016/S0273-1177(03)00465-4}}</ref> , Nickolaenko et al. [2003] <ref name=" Nickolaenko 03">{{cite journal | author= Nickolaenko A. P., B. P. Besser, K. Schwingenschuh | title= Model computations of Schumann resonance on Titan | journal= Planet. Space Sci. | volume= 51(13) | year=2003| pages= 853–862 | doi= 10.1016/S0032-0633(03)00119-3}}</ref> and Pechony and Price [2004] <ref name=" Pechony Price 04">{{cite journal | author= Pechony, O., C. Price | title= Schumann resonance parameters calculated with a partially uniform knee model on Earth, Venus, Mars, and Titan | journal= Radio Sci.| volume= 39(5)| year=2004 | doi= 10.1029/2004RS003056 | pages= RS5007 | unused_data= |RS5007, doi=10.1029/2004RS003056}}</ref> . It appears that only the first Schumann resonance mode might be detectable on [[Titan]].
[[Jupiter]] is the only planet where [[lightning]] activity has been optically detected. Existence of [[lightning]] activity on this planet was predicted by Bar-Nun [1975] <ref name=" Bar-Nun ">{{cite journal | author= Bar-Nun A. | title= Thunderstorms on Jupiter | journal= ICARUS | volume= 24| year=1975| pages = 86–94 | doi= 10.1016/0019-1035(75)90162-1}}</ref> and it is now supported by data from [[Galileo (spacecraft)|Galileo]], [[Voyager program|Voyagers]] 1 and 2, [[Pioneer program|Pioneers]] 10 and 11 and Cassini. [[Saturn]] is also expected to have intensive [[lightning]] activity, but the three visiting spacecrafts – [[Pioneer 11]] in 1979, [[Voyager 1]] in 1980 and [[Voyager 2]] in 1981, failed to provide any convincing evidence from optical observations. The strong storm monitored on [[Saturn]] by the [[Cassini spacecraft]] produced no visible [[lightning]] flashes, although electromagnetic sensors aboard the spacecraft detected signatures that are characteristic of lightning. Little is known about the electrical parameters of [[Jupiter]] and [[Saturn]] interior. Even the question of what should serve as the lower [[waveguide]] boundary is a non-trivial one in case of the gaseous planets. There seem to be no works dedicated to Schumann resonances on [[Saturn]]. Up to date there has been only one attempt to model Schumann resonances on [[Jupiter]] <ref name=" Sentman ">{{cite journal | author= Sentman D. D. | title= Electrical conductivity of Jupiter's Shallow interior and the formation of a resonant planetary-ionosphere cavity | journal= ICARUS | volume= 88| year=1990| pages = 73–86 | doi= 10.1016/0019-1035(90)90177-B}}</ref>, where the lower conducting boundary within the gaseous atmosphere was modeled using a thermodynamic approach. Given the intense lightning activity at Jupiter, the Schumann resonances should be easily detectable with a sensor suitably located within the planetary-ionospheric cavity.
==See also==
*[[Earth's magnetic field]]
*[[Plasma (physics)]]
*[[radiant energy]]
*[[Telluric current]]
==References==
{{reflist}}
==External articles and references==
; General references
*Articles on the NASA ADS Database: [http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&db_key=PRE&qform=AST&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=%22Schumann+Resonances%22&txt_logic=OR&text=&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1 Full list] | [http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&db_key=PRE&qform=AST&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=%22Schumann+Resonances%22&txt_logic=OR&text=&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=YES&gif_link=YES&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1 Full text]
;Websites
* [http://www.oulu.fi/~spaceweb/textbook/schumann.html Schumann resonance reference] from [[University of Oulu]]
* [http://nigec.ucdavis.edu/publications/ar/annual95/northeast/project07.html Schumann Resonance Measurements as a Sensitive Diagnostic for Global Change] (fixed)
* [http://147.175.143.11/ Schumann resonances, experimental results, electric component]
* [http://quake.geo.berkeley.edu/ncedc/em.intro.html Magnetic activity and Schumann resonance]
* [http://www.iihr.uiowa.edu/projects/schumann/Index.html Well illustrated study from the University of Iowa] explaining the construction of a ULF receiver for studying Schumann resonances.
[[Category:Geophysics]]
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