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| [[File:Schumann resonance animation.ogv|thumb|450px|Animation of Schumann resonance in Earth's atmosphere.]]
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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's surface and the [[ionosphere]].
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| == Description ==
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| This global electromagnetic resonance phenomenon is named after physicist [[Winfried Otto Schumann]] who predicted it mathematically in 1952. Schumann resonances occur because the space between the surface of the Earth and the conductive ionosphere acts as a closed [[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 electric currents in lightning. Schumann resonances are the principal background in the electromagnetic spectrum<ref name=MacGorman>MacGorman, W. D. Rust, W. David Rust. "The electrical nature of storms". [http://books.google.com/books?id=_NbHNj7KJecC&pg=PA114 Page 114].</ref> beginning at 3 Hz and extend to 60 Hz,<ref>Handbook of atmospheric electrodynamics, Volume 1 By Hans Volland. Page 277.</ref> and appear as distinct peaks at extremely low frequencies (ELF) around 7.83 (fundamental),<ref>{{cite arXiv |last=Rusov |first=V.D. |eprint=1208.4970 |title=Can Resonant Oscillations of the Earth Ionosphere Influence the Human Brain Biorhythm? |class=physics.gen-ph |year=2012}} Department of Theoretical and Experimental Nuclear Physics, Odessa National Polytechnic University, Ukraine</ref> 14.3, 20.8, 27.3 and 33.8 Hz.<ref name=MacGorman/><ref>Recent advances in multidisciplinary applied physics By A. Méndez-Vilas. Page 65.</ref>
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| In the normal mode descriptions of Schumann resonances, the [[Fundamental frequency|fundamental mode]] 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 7.83 Hz, but this frequency can vary slightly from a variety of factors, such as solar-induced perturbations to the ionosphere, which comprises the upper wall of the closed cavity.{{citation needed|date=March 2011}} The higher resonance modes are spaced at approximately 6.5 Hz intervals,{{citation needed|date=March 2011}} 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 8th partial lies at approximately 60 Hz.{{citation needed|date=March 2011}}
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| Observations of Schumann resonances have been used to track global lightning activity. Owing to the connection between lightning activity and the Earth's climate it has been suggested that they may also be used to monitor global temperature variations and variations of water vapor in the upper troposphere. It has been speculated that extraterrestrial lightning (on other planets) may also be detected and studied by means of their Schumann resonance signatures. Schumann resonances have been used to study the lower ionosphere on Earth and it has been suggested as one way to explore the lower ionosphere on celestial bodies. Effects on Schumann resonances have been reported following geomagnetic and ionospheric disturbances. More recently, discrete Schumann resonance excitations have been linked to [[transient luminous event]]s – [[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]].
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| == History ==
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| In 1893, [[George Francis FitzGerald]] noted that the upper layers of the atmosphere must be fairly good conductors. Assuming that the height of these layers are about 100 km above ground, he estimated that oscillations (in this case the lowest mode of the Schumann resonances) would have a period of 0.1 second.<ref>G. F. FitzGerald, “On the period of vibration of electrical disturbances upon the Earth,” Br. Assoc. Adv. Sci., Rep. 63, 682 (1893)</ref> Because of this contribution, it has been suggested to rename these resonances as Schumann–FitzGerald resonances.<ref>J. D. Jackson, Examples of the zeroth theorem of the history of science, American Journal of Physics, Vol. 76, No. 8, pp. 704–719, August 2008</ref> However FitzGerald's findings were not widely known as they were only presented at a meeting of the British Association for the Advancement of Science, followed by a brief mention in a column in Nature.
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| Hence the first suggestion that an ionosphere existed, capable of trapping [[electromagnetic waves]], is attributed to [[Heaviside]] and Kennelly (1902).<ref name="Heaviside 1902">{{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 1902">{{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 1925">{{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. Series A, Containing Papers of a Mathematical and Physical Character |volume=109 |year=1925 |pages=621–641 |doi=10.1098/rspa.1925.0149 |issue=752|bibcode=1925RSPSA.109..621A }}</ref> were able to prove experimentally the existence of the ionosphere.
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| Although some of the most important mathematical tools for dealing with spherical [[waveguide]]s were developed by [[G. N. Watson]] in 1918,<ref name="Watson">{{cite journal |author=Watson, G.N. |title=The diffraction of electric waves by the Earth |journal=Proceedings of the Royal Society |volume=Ser.A 95 |year=1918| pages=83–99}}</ref> it was [[Winfried Otto Schumann]] who first studied the theoretical aspects of the global resonances of the earth–ionosphere [[waveguide]] system, known today as the Schumann resonances. In 1952–1954 Schumann, together with [[H. L. König]], attempted to measure the resonant frequencies.<ref name="Schumann 1952a">{{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|bibcode=1952ZNatA...7..149S }}</ref><ref name="Schumann 1952b">{{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|bibcode=1952ZNatA...7..250S }}</ref><ref name="Schumann 1952c">{{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 |issue=12}}</ref><ref name="Schumann 1954d">{{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 |bibcode=1954NW.....41..183S |issue=8}}</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|bibcode=1960Natur.188..638B |issue=4751}}</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 |bibcode=1962JGR....67..619B |issue=2}}</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 |bibcode=1962JGR....67.4081B |issue=10}}</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.
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| == Basic theory ==
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| Lightning discharges are considered to be the primary natural source of Schumann resonance excitation; lightning channels behave like huge antennas that radiate [[electromagnetic energy]] at frequencies below about 100 kHz.<ref name="Volland 1984">{{cite book |author=Volland, H. |title=Atmospheric Electrodynamics |publisher=Springer-Verlag, Berlin |year=1984}}</ref> These signals are very weak at large distances from the lightning source, 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 1984"/>
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| 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 1952a"/>
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| :<math>f_{n} =\frac{c}{2 \pi a}\sqrt{n(n+1)}</math>
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| The real Earth–ionosphere [[waveguide]] is not a perfect electromagnetic resonant cavity. Losses due to finite ionosphere [[electrical conductivity]] lower the propagation speed of electromagnetic signals in the cavity, resulting in a resonance frequency that is lower 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 difference in the height of the ionosphere, latitudinal changes in the [[Earth's magnetic field]], sudden ionospheric disturbances, polar cap absorption, variation in the [[Earth radius]] of +/- 11 km from equator to geographic poles, etc. that produce other effects in the Schumann resonance power spectra.
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| == Measurements ==
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| Today Schumann resonances are recorded at many separate research stations around the world. The sensors used to measure Schumann resonances typically consist of two horizontal [[magnetic inductive coil]]s for measuring the north-south and east-west components of the [[magnetic field]], and a vertical electric dipole antenna for measuring the vertical component of the [[electric field]]. A typical passband of the instruments is 3–100 Hz. The Schumann resonance electric field amplitude (~300 microvolts per meter) is much smaller than the [[Fair weather condition|static fair-weather electric field]] (~150 V/m) in the [[atmosphere]]. Similarly, the amplitude of the Schumann resonance magnetic field (~1 picotesla) is many [[orders of magnitude]] smaller than the [[Earth's magnetic field]] (~30–50 microteslas).<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> Specialized receivers and antennas are needed to detect and record 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 [[induction coil]]s typically consist of tens- to hundreds-of-thousands of turns of wire wound around a core of very high [[magnetic permeability]].
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| === Dependence on global lightning activity === | |
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| From the very beginning of Schumann resonance studies, it was known that they could be used to monitor global lightning activity. At any given time there are about 2000 [[thunderstorms]] around the [[globe]].<ref name="Heckman 1998">{{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 |bibcode=1998JGR...10331775H}}</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 |bibcode=2003JGRD..108.4005C}}</ref> these [[thunderstorms]] create the background Schumann resonance signal.
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| Determining the spatial lightning distribution from Schumann resonance records is a complex problem: in order to 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, based on the known properties of lightning [[climatology]]. An alternative approach is placing the receiver at the [[North Pole|North]] or [[South Pole]], which remain approximately [[equidistant]] from the main thunderstorm centers during the day.<ref name="Nickolaenko 1997">{{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 2001">{{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 combination. This technique assumes the cavity is spherically symmetric and therefore does not include known cavity asymmetries that are believed to affect the resonance and propagation properties of electromagnetic waves in the system.
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| ==== Diurnal variations ====
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| The best documented and the most debated features of the Schumann resonance phenomenon are the diurnal variations of the background Schumann resonance power spectrum. | |
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| 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]] is independent of the direction of the source relative to the observer, and is therefore a measure of global lightning. The diurnal behavior of the vertical electric field shows three distinct 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.
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| ===== "Chimney" ranking =====
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| 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. Schumann resonance observations made from Europe 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 "/> although observations made from North America indicate the dominant contribution comes from South America. The reason for such disparity remains unclear, but may have something to do with the 60 Hz cycling of electricity used in North America (60 Hz being a mode of Schumann Resonance). 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. It was assumed that the distribution of lightning in the satellite maps was a good proxy for Schumann excitations sources, even though satellite observations predominantly measure in-cloud lightning rather than the cloud-to-ground lightning that are the primary exciters of the resonances. 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.
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| ===== Influence of the day-night asymmetry =====
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| 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"/> 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 1965">{{cite journal |author=Madden T., W. Thompson |title=Low-frequency electromagnetic oscillations of the Earth–ionosphere cavity |journal=Rev. Geophys. |volume=3 |year=1965| pages=211 |doi=10.1029/RG003i002p00211 |issue=2 |bibcode=1965RvGSP...3..211M}}</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 |publisher=Kluwer Academic Publishers, Dordrecht-Boston-London |year=2002 |title=Resonances in the Earth–ionosphere cavity}}</ref>
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| The interest in the influence of the day-night asymmetry in the ionosphere conductivity on Schumann resonances gained 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 |year=1991 |pages=15973–15984 |doi=10.1029/91JA01085 |issue=9 |bibcode=1991JGR....9615973S}}</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 that were widely separated in longitude. They interpreted the diurnal variations observed at each station in terms of a combination of a diurnally varying global excitation modulated by the local ionosphere height. Their work, which combined both observations and energy conservation arguments, convinced many scientists of 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 uniquely interpreted solely 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=42 |year=2006 |doi=10.1029/2006RS003455 |pages=RS2S05 |issue=2 |bibcode=2006RaSc...41.2S05P}}</ref>
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| 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 "/> 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="Pechony et al."/><ref name="Nick 2002"/> 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="Pechony et al."/><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 |issue=2 |year=2007 |doi=10.1029/2005RS003402 |pages=RS2S14 |bibcode=2006RaSc...41.2S14Y}}</ref>
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| 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. Part of this controversy stems from the fact that the Schumann resonance parameters extractable from observations provide only a limited amount of information about the coupled lightning source-ionospheric system geometry. The problem of inverting observations to simultaneously infer both the lightning source function and ionospheric structure is therefore extremely underdetermined, leading to the possibility of nonunique interpretations.
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| ==== The "inverse problem" ====
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| 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 because the mean rate of excitation by lightning, ~50 lightning events per second globally, mixes up the individual contributions together. However, occasionally there occur extremely large lightning flashes which produce distinctive signatures that stand out from the background signals. Called "Q-bursts", they are produced by intense lightning strikes that transfer large amounts of charge from clouds to the ground, and often carry high peak current.<ref name="Ogawa"/> Q-bursts can exceed the [[amplitude]] of the background signal level by a factor of 10 or more, and appear with intervals of ~10 s,<ref name="Shvets 2001"/> 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, and requires assuming a model for the Earth–ionosphere cavity. The multi-station techniques are more accurate, but require more complicated and expensive facilities.
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| === Transient luminous events research ===
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| It is now believed that many of the Schumann resonances transients (Q bursts) are related to the [[Upper-atmospheric lightning|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 |issue=5227|bibcode=1995Sci...269.1088B }}</ref> showed that [[Sprite (lightning)|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"/><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 |page=L20107 |year=2004 |doi=10.1029/2004GL020711}}</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 2002">{{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 |year=2002 |pages=1279 |doi=10.1029/2001GL014593 |issue=8 |bibcode=2002GeoRL..29h.120H}}</ref>
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| ==== Global temperature ====
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| Williams [1992]<ref name="Williams 1992">{{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 |issue=5060 |bibcode=1992Sci...256.1184W }}</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 1992"/> 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 1989">{{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 |bibcode=1989JGR....9413151W}}</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. A strong link between global lightning and global temperature has not been experimentally confirmed as of 2008.
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| ==== Upper tropospheric water vapor ====
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| 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 1984">{{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 1998">{{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 |issue=5380}}</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 2000">{{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 |pmid=10917527 |issue=6793}}</ref> suggested that changes in the UTWV can be derived from records of Schumann Resonances.
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| According to the effective work made by the Upper Tropospheric Water Vapor (( UTWV )), we should highlight that the percentage of UTWV in normal condition of the Air mass can be meauserd as a minimal quantity, so that its influence can be considered very very low; in fact the higher percentage of it can be only found in the lower Tropspheric layers. But in the case of a high quantity of UTWV in the highest level of Troposphere, due to a warmer air mass of atlantic origins, for istance, the Water vapor, due to the low air temperature ((about minus 60 Degrees )) it turns into ice cristal, becoming clouds as Cirrus or Cirrus Stratus: no Water vapour exists as gas with so low temperature. So, we can say that the affirmation that Water vapor interacts with cloud, can be considered wrong as the clouds both those of low level of ((Atmosphere)) and those of higher levels of it are made of condensed or cristallised Water Vapor.
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| == On other planets and moons ==
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| The existence of Schumann-like resonances is conditioned primarily by two factors:
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| # A closed, planetary-sized spherical{{dubious|date=March 2011}} cavity, consisting of conducting lower and upper boundaries separated by an insulating medium. For the earth the conducting lower boundary is its surface, and the upper boundary is the ionosphere. Other planets may have similar electrical conductivity geometry, so it is speculated that they should possess similar resonant behavior.
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| # A source of electrical excitation of [[electromagnetic waves]] in the ELF range.
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| Within the [[Solar System]] there are five candidates for Schumann resonance detection besides the Earth: [[Venus]], [[Mars]], [[Jupiter]], [[Saturn]] and its biggest moon [[Titan (moon)|Titan]].
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| Modeling Schumann resonances on the planets and [[moons]] of the Solar System is complicated by the lack of knowledge of the [[waveguide]] parameters. No in situ capability exists today to validate the results.
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| === Venus ===
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| The strongest evidence for lightning on Venus comes from the impulsive electromagnetic waves detected by [[Venera]] 11 and 12 landers. Theoretical calculations of the Schumann resonances at Venus were reported 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 2004">{{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| year=2004 |doi=10.1029/2004RS003056 |pages=RS5007 |issue=5 |bibcode=2004RaSc...39.5007P}}</ref> Both studies yielded very close results, indicating that Schumann resonances should be easily detectable on that planet given a lightning source of excitation and a suitably located sensor.
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| === Mars ===
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| <!-- ToDo: reduce redundancy --> | |
| In the case of Mars there have been terrestrial observations of radio emission spectra that have been associated with Schumann resonances.<ref name="Ruf" /> The reported radio emissions are not of the primary electromagnetic Schumann modes, but rather of secondary modulations of the nonthermal microwave emissions from the planet at approximately the expected Schumann frequencies, and have not been independently confirmed to be associated with lightning activity on Mars. There is the possibility that future lander missions could carry in situ instrumentation to perform the necessary measurements. Theoretical studies are primarily directed to parameterizing the problem for future planetary explorers.
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| Detection of lightning activity on Mars has been reported by Ruf et al. [2009].<ref name="Ruf">{{cite journal |author=Ruf, C., N. O. Renno, J. F. Kok, E. Bandelier, M. J. Sander, S. Gross, L. Skjerve, and B. Cantor |title=Emission of Non-thermal Microwave Radiation by a Martian Dust Storm |journal=Geophys. Res. Lett. |volume=36 |year=2009 |pages=L13202 |doi=10.1029/2009GL038715 |bibcode=2009GeoRL..3613202R |issue=13}}</ref> The evidence is indirect and in the form of modulations of the nonthermal microwave spectrum at approximately the expected Schumann resonance frequencies. It has not been independently confirmed that these are associated with electrical discharges on Mars. In the event confirmation is made by direct, in situ observations, it would verify the suggestion of the possibility of charge separation and lightning strokes in the Martian dust storms made by Eden and Vonnegut [1973]<ref name="Eden 1973">{{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=962–3 |doi=10.1126/science.180.4089.962 |pmid=17735929 |issue=4089|bibcode=1973Sci...180..962E }}</ref> and Renno et al. [2003].<ref name="Renno 2003">{{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| year=2003| pages=2140 |doi=10.1029/2003GL017879 |issue=22 |bibcode=2003GeoRL..30vPLA1R}}</ref> Martian global resonances were modeled by Sukhorukov [1991],<ref name="Sukhorukov 1991">{{cite journal |author=Sukhorukov A. I. |title=On the Schumann resonances on Mars |journal=Planet. Space Sci.| volume= 39 |year=1991| pages=1673–1676 |doi=10.1016/0032-0633(91)90028-9 |issue=12|bibcode=1991P&SS...39.1673S }}</ref> Pechony and Price [2004]<ref name="Pechony Price 2004"/> 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 |bibcode=2006RaSc...41.1003M}}</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. Evidence of the first three Schumann resonance modes is present in the spectra of radio emission from the lightning detected in Martian dust storms.<ref name="Ruf"/>
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| === Titan ===
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| It was long ago suggested that lightning discharges may occur on Titan,<ref name="Lammer 2001">{{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 |bibcode=2001P&SS...49..561L |issue=6}}</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 have received more attention than on any other celestial body, in works by Besser et al. [2002],<ref name="Besser 2002">{{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, September 16–19 |year=2002 }}</ref> Morente et al. [2003],<ref name="Morente 2003">{{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 |bibcode=2003Icar..162..374M |issue=2}}</ref> Molina-Cuberos et al. [2004],<ref name="Molina-Cuberos 2004">{{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 |bibcode=2004AdSpR..33.2309M |issue=12 }}</ref> Nickolaenko et al. [2003]<ref name="Nickolaenko 2003">{{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 |year=2003| pages=853–862 |doi=10.1016/S0032-0633(03)00119-3 |issue=13 |bibcode=2003P&SS...51..853N}}</ref> and Pechony and Price [2004].<ref name="Pechony Price 2004"/> It appears that only the first Schumann resonance mode might be detectable on Titan.
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| Since the landing of the Huygens probe on Titan's surface in January 2005, there have been many reports on observations and theory of an atypical Schumann resonance on Titan. After several tens of fly-bys by Cassini, neither lightning nor thunderstorms were detected in Titan's atmosphere. Scientists therefore proposed another source of electrical excitation: induction of ionospheric currents by Saturn's co-rotating magnetosphere. All data and theoretical models comply with a Schumann resonance, the second eigenmode of which was observed by the Huygens probe. The most important result of this is the proof of existence of a buried liquid water-ammonia ocean under few tens of km the icy subsurface crust.<ref>
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| Béghin, C., et al., 2007. A Schumann-like resonance on Titan driven by Saturn’s magnetosphere possibly revealed by the Huygens Probe, Icarus 191, 251-266.
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| </ref><ref>
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| Béghin, C., et al., 2009. New insights on Titan’s plasma-driven Schumann resonance inferred from Huygens and Cassini data, Planet. Space Sci., 57, 1872-1888.
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| </ref><ref>
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| Béghin, C., Hamelin, M., Sotin, C., 2010. Titan’s native ocean revealed beneath some 45 km of ice by a Schumann-like resonance, Comptes Rendus Geoscience, 342, 425-433.
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| </ref><ref>
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| Béghin, C., and 8 colleagues. Analytic theory of Titan’s Schumann resonance: Constraints on ionospheric conductivity and buried water ocean, Icarus, 218, 1028-1042, 2012.</ref>
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| <!-- ToDo: verify refs, assign to statements, format, find independent sources -->
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| === Jupiter and Saturn ===
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| Jupiter is one planet where lightning activity has been optically detected. Existence of lightning activity on that 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 |bibcode=1975Icar...24...86B}}</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 confirmed to have lightning activity.<ref>http://www.ciclops.org/view_event/178/Lightning_Flashing_in_Daylight</ref> Though three visiting spacecraft – [[Pioneer 11]] in 1979, [[Voyager 1]] in 1980 and [[Voyager 2]] in 1981, failed to provide any convincing evidence from optical observations, in July 2012 the Cassini spacecraft detected visible lightning flashes, and 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. To date there has been only one attempt to model Schumann resonances on Jupiter.<ref name="Sentman 1990">{{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 |bibcode=1990Icar...88...73S}}</ref> Here, the electrical conductivity profile within the gaseous atmosphere of Jupiter was calculated using methods similar to those used to model stellar interiors, and it was pointed out that the same methods could be easily extended to the other gas giants Saturn, Uranus and Neptune. Given the intense lightning activity at Jupiter, the Schumann resonances should be easily detectable with a sensor suitably positioned within the planetary-ionospheric cavity.
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| == See also ==
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| *[[Earth's magnetic field]]
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| *[[Plasma (physics)]]
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| *[[radiant energy]]
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| *[[Telluric current]]
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| *[[The Hum]]
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| *[[Cymatics]]
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| == References ==
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| {{Reflist}}
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| == External articles and references ==
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| ; General references
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| *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]
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| ;Websites
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| * [http://quake.geo.berkeley.edu/ncedc/em.intro.html Magnetic activity and Schumann resonance]
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| * [http://www.iaspacegrant.org/sites/default/files/pdf_files/Kruger-SEED.pdf Well illustrated study from the University of Iowa explaining the construction of a ULF receiver for studying Schumann resonances. Link updated 3 Nov. 2011]
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| * [http://www.glcoherence.org/monitoring-system/live-data.html Global Coherence Initiative (Spectrogram Calendar)] Schumann resonance live data
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| ; Animation
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| * [http://svs.gsfc.nasa.gov/vis/a010000/a010800/a010891/ Schumann resonance animation] from [[NASA Goddard Space Flight Center]]
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| {{DEFAULTSORT:Schumann Resonances}}
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| [[Category:Atmospheric electricity]]
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| [[Category:Electromagnetic radiation]]
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| [[Category:Ionosphere]]
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