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{{Short description|Global electromagnetic resonances, generated and excited by lightning discharges}}{{Use mdy dates|date=July 2019}}
[[File:Schumann resonance animation.ogv|thumb|450px|A simplified artistic animation of Schumann resonance in Earth's atmosphere.]]
[[File:Schumann resonance (EN).svg|thumb|275x275px|A diagram of Schumann resonances in Earth's atmosphere]]
The '''Schumann resonances''' ('''SR''') are a set of spectral peaks in the [[extremely low frequency]] portion of the [[Earth]]'s [[electromagnetic field]] spectrum. Schumann resonances are global electromagnetic [[resonance]]s,  generated and excited by [[lightning]] discharges in the cavity formed by the Earth's surface and the [[ionosphere]].<ref>{{Cite web |url=http://www.nasa.gov/mission_pages/sunearth/news/gallery/schumann-resonance.html |title=Schumann Resonance |publisher=NASA |language=en |access-date=2017-11-08}}</ref>

== Description ==
The global electromagnetic resonance phenomenon is named after physicist [[Winfried Otto Schumann]] who predicted it mathematically in 1952.
Schumann resonances are the principal background in the part of the electromagnetic spectrum<ref>{{cite book |last1=MacGorman |first1=D.R. |last2=Rust |first2=W. D. |year=1998 |title=The Electrical Nature of Storms |publisher=Oxford University Press |isbn=9780195073379 |location=New York, NY |page=114 |oclc=35183896 |url={{google books |plainurl=yes |id=_NbHNj7KJecC |page=114}}}}</ref> from 3&nbsp;Hz through 60&nbsp;Hz<ref>{{cite book |last=Volland |first=Hans |year=1995 |title=Handbook of Atmospheric Electrodynamics |volume=1 |page=277 |publisher=CRC Press |isbn=9780849386473 |place=Boca Raton, FL |oclc=31408654}}</ref> and appear as distinct peaks at extremely low frequencies around 7.83&nbsp;Hz (fundamental), 14.3, 20.8, 27.3, and 33.8&nbsp;Hz.<ref>{{cite conference |last1=Montiel |first1=I. |last2=Bardasano |first2=J.L. |last3=Ramos |first3=J.L. |publication-date=2005 |title=Biophysical device for the treatment of neurodegenerative diseases |editor-last=Méndez-Vilas |editor-first=A. |book-title=Recent Advances in Multidisciplinary Applied Physics |pages=63–69 |conference=The First International Meeting on Applied Physics (APHYS-2003) |date=13–18 October 2003 |place=Badajoz, ES |doi=10.1016/B978-008044648-6.50011-2 |isbn=9780080446486 }}</ref>

Schumann resonances occur because the space between the surface of the Earth and the conductive ionosphere acts as a closed, although variable-sized, [[waveguide]]. The limited dimensions of the Earth cause this waveguide to act as a [[resonant cavity]] for [[electromagnetic waves]] in the extremely low frequency band. The cavity is naturally excited by electric currents in lightning.

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. The lowest-frequency mode has the highest intensity, and the frequency of all modes can vary slightly owing to solar-induced perturbations to the ionosphere (which compress the upper wall of the closed cavity){{citation needed|date=March 2011}} amongst other factors. The higher resonance modes are spaced at approximately 6.5&nbsp;Hz intervals (as may be seen by feeding numbers into the [[#Basic theory|formula]]), a characteristic attributed to the atmosphere's spherical geometry. The peaks exhibit a spectral width of approximately 20% due to the damping of the respective modes in the dissipative cavity.{{Cn|date=August 2021}}

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 be used to monitor global temperature variations and variations of water vapor in the upper troposphere. 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.<ref name=Williams/><ref name=Barr2/> Some have proposed that lightning on other planets might be detectable and studied by means of Schumann resonance signatures of those planets.<ref name=Williams/><ref name=Barr2/>

Effects on Schumann resonances have been reported following geomagnetic and ionospheric disturbances. More recently, discrete Schumann resonance excitation has 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]].{{citation needed|date=July 2014}} A new field of interest using Schumann resonances is related to short-term [[earthquake prediction]].{{citation needed|date=July 2014}}  

Interest in Schumann resonances renewed in 1993 when E.R.&nbsp;Williams showed a correlation between the resonance frequency and tropical air temperatures, suggesting the resonance could be used to monitor [[global warming]].<ref name=Williams>{{cite journal |last=Williams |first=Earle R. |date=May 22, 1992 |title=The Schumann resonance: A global tropical thermometer |journal=Science |volume=256 |issue=5060 |pages=1184–1187 |bibcode=1992Sci...256.1184W |doi=10.1126/science.256.5060.1184 |pmid=17795213 |s2cid=26708495 }}</ref><ref name=Barr2>{{cite journal |last1=Barr |first1=R. |last2=Llanwyn Jones |first2=David |last3=Rodger |first3=C.J. |year=2000 |title=ELF and VLF radio waves |journal=[[Journal of Atmospheric and Solar-Terrestrial Physics]] |volume=62 |issue=17–18 |pages=1689–1718 |bibcode=2000JASTP..62.1689B |doi=10.1016/S1364-6826(00)00121-8 |url=http://nova.stanford.edu/~vlf/IHY_Test/Tutorials/SubionosphericVLFPropagation/Papers/Barr_2000.pdf |access-date=May 6, 2017 |archive-date=April 5, 2014 |archive-url=https://web.archive.org/web/20140405051019/http://nova.stanford.edu/~vlf/IHY_Test/Tutorials/SubionosphericVLFPropagation/Papers/Barr_2000.pdf |url-status=dead }}</ref> In [[geophysical survey]], Schumann resonances are used to locate offshore hydrocarbon deposits.<ref>{{cite book |last=Sainson |first=Stéphane |date=2017 |title=Electromagnetic seabed logging: A new tool for geoscientists |publisher=Springer |isbn=978-3-319-45355-2}}</ref>{{page needed|date=January 2020}}

== History ==
{{More citations needed|section|date=July 2021}}
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 is about 100&nbsp;km above ground, he estimated that oscillations (in this case the lowest [[Mode (music)|mode]] of the Schumann resonances) would have a period of 0.1 second.<ref>{{Cite journal |last=FitzGerald |first=G. F. |author-link=George Francis FitzGerald |date=1893 |title=On the period of vibration of electrical disturbances upon the Earth |url=https://www.biodiversitylibrary.org/item/95445#page/800/mode/1up |journal=Report of the British Association for the Advancement of Science |volume=63rd Meeting |page=682}}</ref> Because of this contribution, it has been suggested to rename these resonances "Schumann–FitzGerald resonances".<ref>{{cite journal|first=J. D. |last=Jackson |title=Examples of the zeroth theorem of the history of science |journal=American Journal of Physics |volume=76 |issue=8 |pages=704–719 |date=August 2008 |url=http://www-theory.lbl.gov/jdj/ZerothT_AJP.pdf|arxiv = 0708.4249 |bibcode = 2008AmJPh..76..704J |doi = 10.1119/1.2904468 |s2cid=117774134 }}</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''.<ref>{{cite journal |last1=(Staff) |title=Physics at the British Association |journal=Nature |date=September 28, 1893 |volume=48 |issue=1248 |pages=525 - 529 |url=https://archive.org/details/naturelond48londuoft/page/526/mode/2up}}  See especially p. 526.</ref>

The first suggestion that an ionosphere existed, capable of trapping [[electromagnetic waves]], is attributed to [[Heaviside]] and [[Arthur E. Kennelly|Kennelly]] (1902).<ref name="Heaviside 1902">{{Cite encyclopedia |title=Telegraphy, Sect. 1, Theory |encyclopedia=Encyclopædia Britannica |location=London |last=Heaviside |first=O. |date=1902 |edition=10 |volume=9 |pages=213–218}}</ref><ref name="Kennelly 1902">{{Cite journal |last=Kennelly |first=Arthur E. |date=March 15, 1902 |title=On the elevation of the electrically-conducting strata of the earth's atmosphere |journal=Electrical World and Engineer |volume=39 |issue=11 |pages=473|url=https://babel.hathitrust.org/cgi/pt?id=uva.x002225471&seq=491 }}</ref> It took another twenty years before [[Edward Victor Appleton|Edward Appleton]] and Barnett in 1925<ref name="Appleton 1925">{{cite journal |last1=Appleton|first1=E. V. |first2=M. A. F. |last2=Barnett |title=On Some Direct Evidence for Downward Atmospheric Reflection of Electric Rays |journal=Proceedings of the Royal Society of London A |volume=109 |date=1925 |pages=621–641 |doi=10.1098/rspa.1925.0149 |issue=752|bibcode=1925RSPSA.109..621A |doi-access=free }}</ref> were able to prove experimentally the existence of the ionosphere.

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 |last=Watson|first=G. N. |title=The diffraction of electric waves by the Earth |journal=Proceedings of the Royal Society of London A |volume=95 |issue=666 |date=1918| pages=83–99|bibcode=1918RSPSA..95...83W|doi=10.1098/rspa.1918.0050|doi-access=free}}</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 [[Herbert L. König|H. L. König]], attempted to measure the resonant frequencies.<ref name="Schumann 1952a">{{cite journal |last=Schumann |first=W. O. |title=Über die strahlungslosen Eigenschwingungen einer leitenden Kugel, die von einer Luftschicht und einer Ionosphärenhülle umgeben ist |trans-title=On the radiationless natural oscillations of a conducting sphere which is surrounded by a layer of air and an ionospheric shell |journal=Zeitschrift für Naturforschung A |volume=7 |issue=2 |date=1952| pages=149–154|bibcode=1952ZNatA...7..149S |doi = 10.1515/zna-1952-0202 |s2cid=96060996 |language=De }}</ref><ref name="Schumann 1952b">{{cite journal |last=Schumann |first=W. O. |title=Über die Dämpfung der elektromagnetischen Eigenschwingungen des Systems Erde – Luft – Ionosphäre |trans-title=On the damping of the natural electromagnetic oscillations of the earth-air-ionosphere system |journal=Zeitschrift für Naturforschung A |volume=7 |issue=3–4 |date=1952| pages=250–252|bibcode=1952ZNatA...7..250S |doi = 10.1515/zna-1952-3-404 |doi-access=free |language= De }}</ref><ref name="Schumann 1952c">{{cite journal |last=Schumann |first=W. O. |title=Über die Ausbreitung sehr Langer elektrischer Wellen um die Signale des Blitzes |trans-title=On the propagation of very long electrical waves around signals from lightning |journal=Nuovo Cimento |volume=9 |date=1952| pages=1116–1138 |doi=10.1007/BF02782924 |issue=12|bibcode=1952NCim....9.1116S |s2cid=122643775 |language=De }}</ref><ref name="Schumann 1954d">{{cite journal |last1=Schumann |first1= W. O.|first2=H. |last2=König|title=Über die Beobachtung von Atmospherics bei geringsten Frequenzen |trans-title=On the observation of atmospherics at lowest frequencies |journal=Naturwissenschaften |volume=41 |date=1954| pages=183–184 |doi=10.1007/BF00638174 |bibcode=1954NW.....41..183S |issue=8|s2cid= 6546863|language=De }}</ref> However, it was not until measurements made by Balser and Wagner in 1960–1963<ref name="Balser Wagner a">{{cite journal |last1=Balser |first1=M.|first2=C. |last2=Wagner|title=Measurement of the spectrum of radio noise from 50 to 100 c/s |journal=Journal of Research of the National Bureau of Standards |volume=64D |issue=4|date=1960 |pages=415–418 |doi=10.6028/jres.064d.050|doi-access=free }}</ref><ref name="Balser Wagner b">{{cite journal |last1=Balser |first1=M.|first2=C. |last2=Wagner|title=Observations of Earth–ionosphere cavity resonances |journal=Nature |volume=188 |date=1960 |pages=638–641 |doi=10.1038/188638a0|bibcode=1960Natur.188..638B |issue=4751|s2cid=31089734}}</ref><ref name="Balser Wagner c">{{cite journal |last1=Balser |first1=M.|first2=C. |last2=Wagner|title=Diurnal power variations of the Earth–ionosphere cavity modes and their relationship to worldwide thunderstorm activity |journal=Journal of Geophysical Research |volume=67 |date=1962 |pages=619–625 |doi=10.1029/JZ067i002p00619 |bibcode=1962JGR....67..619B |issue=2}}</ref><ref name="Balser Wagner d">{{cite journal |last1=Balser |first1=M.|first2=C. |last2=Wagner|title=On frequency variations of the Earth–ionosphere cavity modes |journal=Journal of Geophysical Research |volume=67 |date=1962 |pages=4081–4083 |doi=10.1029/JZ067i010p04081 |bibcode=1962JGR....67.4081B |issue=10}}</ref><ref name="Balser Wagner e">{{cite journal |last1=Balser |first1=M.|first2=C. |last2=Wagner|title=Effect of a high-altitude nuclear detonation on the Earth–ionosphere cavity |journal=Journal of Geophysical Research |volume=68 |issue=13|date=1963 |pages=4115–4118 |doi=10.1029/jz068i013p04115|bibcode = 1963JGR....68.4115B }}</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 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&nbsp;kHz.<ref name="Volland 1984">{{cite book |last=Volland|first=H. |title=Atmospheric Electrodynamics |url=https://archive.org/details/trent_0116300004144|url-access=registration|publisher=Springer-Verlag, Berlin |date=1984}}</ref> These signals are very weak at large distances from the lightning source, but the Earth–ionosphere [[waveguide]] behaves like a [[resonator]] at extremely low resonance frequencies.<ref name="Volland 1984"/>

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"/>

:<math>f_{n} =\frac{c}{2 \pi a}\sqrt{n(n+1)}</math>

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&nbsp;km from equator to geographic poles, etc. that produce other effects in the Schumann resonance power spectra.{{Cn|date=August 2021}}

== Measurements ==
{{More citations needed|section|date=July 2021}}
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&nbsp;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]].<ref name="Price et al."/>

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 |last1=Price|first1=C.|first2=O. |last2=Pechony|first3=E. |last3=Greenberg |title=Schumann resonances in lightning research |journal=Journal of Lightning Research |volume=1 |date=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 |last1=Ogawa|first1=T.|first2=Y. |last2=Tanka|first3= T. |last3=Miura|first4=M. |last4=Yasuhara|title=Observations of natural ELF electromagnetic noises by using the ball antennas |journal=Journal of Geomagnetism and Geoelectricity |volume=18 |issue=4|date=1966| pages=443–454 |doi=10.5636/jgg.18.443|bibcode=1966JGG....18..443O|url=https://www.jstage.jst.go.jp/article/jgg1949/18/4/18_4_443/_pdf|doi-access=free}}</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]].

=== Dependence on global lightning activity ===

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 |last1=Heckman |first1=S. J.|first2=E. |last2=Williams |title=Total global lightning inferred from Schumann resonance measurements |journal=Journal of Geophysical Research |volume=103 |issue=D24 |date=1998| pages=31775–31779 |doi=10.1029/98JD02648 |bibcode=1998JGR...10331775H|doi-access=free }}</ref> Producing approximately 50 lightning events per [[second]],<ref name="Christian ">{{cite journal |display-authors=4|last1=Christian |first1=H. J.|first2=R. J. |last2=Blakeslee|first3=D. J. |last3=Boccippio|first4=W. L. |last4=Boeck|first5=D. E. |last5=Buechler|first6=K. T. |last6=Driscoll|first7=S. J. |last7=Goodman|first8=J. M. |last8=Hall|first9=W. J. |last9=Koshak|first10=D. M. |last10=Mach|first11=M. F. |last11=Stewart |title=Global frequency and distribution of lightning as observed from space by the Optical Transient Detector |journal=Journal of Geophysical Research |volume=108 |issue=D1 |date=2003| page=4005 |doi=10.1029/2002JD002347 |bibcode=2003JGRD..108.4005C|doi-access=free }}</ref> these [[thunderstorms]] are directly linked to the background Schumann resonance signal.

Determining the spatial lightning distribution from Schumann resonance records is a complex problem. To estimate the lightning intensity from Schumann resonance records it is necessary to account for both the distance to lightning sources and the wave propagation between the source and the observer. A 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 |last=Nickolaenko|first=A. P. |title=Modern aspects of Schumann resonance studies |journal=Journal of Atmospheric and Solar-Terrestrial Physics |volume=59 |issue=7 |date=1997| pages=806–816 |doi=10.1016/s1364-6826(96)00059-4|bibcode = 1997JASTP..59..805N }}</ref> 

One method not requiring preliminary assumptions on the lightning distribution<ref name="Shvets 2001">{{cite journal |last=Shvets |first=A. V. |title=A technique for reconstruction of global lightning distance profile from background Schumann resonance signal |journal=Journal of Atmospheric and Solar-Terrestrial Physics |volume=63 |issue=10 |date=2001| pages=1061–1074 |doi=10.1016/s1364-6826(01)00024-4|bibcode = 2001JASTP..63.1061S }}</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.

==== 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]] 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: one at 9 UT ([[Universal Time]]) linked to the daily peak of [[thunderstorm]] activity from [[Southeast Asia]]; one at 14 UT linked to the peak of [[Africa]]n lightning activity; and one at 20 UT linked to the peak of [[South America]]n lightning activity. The time and [[amplitude]] of the peaks vary throughout the year, linked to seasonal changes in lightning activity.

===== "Chimney" ranking =====

In general, the African peak is the strongest, reflecting the major contribution of the African "chimney"{{clarification needed|date=July 2023}} to 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, while observations made from North America indicate the dominant contribution comes from South America.

Williams and Sátori<ref name="Williams Satori">{{cite journal |last1=Williams |first1=E. R.|first2=G. |last2=Sátori |title=Lightning, thermodynamic and hydrological comparison of the two tropical continental chimneys |journal=Journal of Atmospheric and Solar-Terrestrial Physics |volume=66 |issue=13–14|date=2004| pages=1213–1231 |doi=10.1016/j.jastp.2004.05.015|bibcode = 2004JASTP..66.1213W }}</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. The "corrected" records presented in the work by Sátori, et al.<ref name="Satori ">{{cite journal |last1=Sátori |first1=G.|first2= M. |last2=Neska|first3=E. |last3=Williams|first4=J. |last4=Szendrői |title=Signatures of the non-uniform Earth–ionosphere cavity in high time-resolution Schumann resonance records |journal=Radio Science |volume=42 |issue=2 |pages=RS003483 |year=2007 |doi=10.1029/2006RS003483|bibcode = 2007RaSc...42.2S10S |doi-access=free }}</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 |last1=Pechony|first1=O.|first2=C. |last2=Price|first3=A. P. |last3=Nickolaenko |title=Relative importance of the day-night asymmetry in Schumann resonance amplitude records |journal=Radio Science |volume=42 |issue=2 |pages=RS2S06 |year=2007 |doi=10.1029/2006RS003456|url=https://zenodo.org/record/1040408|bibcode = 2007RaSc...42.2S06P |s2cid=118326191 }}</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 the same Asia-America chimney ranking.  On the other hand, some optical satellite and climatological lightning data suggest the South American thunderstorm center is stronger than the Asian center.<ref name="Christian "/>

The reason for the disparity among rankings of Asian and American chimneys in Schumann resonance records remains unclear, and is the subject of further 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"/> 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 |last1=Madden |first1=T. |last2=Thompson |first2=W. |date=1965 |title=Low-frequency electromagnetic oscillations of the Earth–ionosphere cavity |journal=Reviews of Geophysics |volume=3 |issue=2 |page=211 |bibcode=1965RvGSP...3..211M |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 |last1=Nickolaenko |first1=A. P.|first2=M. |last2=Hayakawa|publisher=Kluwer Academic Publishers, Dordrecht-Boston-London |date=2002 |title=Resonances in the Earth–ionosphere cavity}}</ref>

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="S">{{Cite journal |last1=Sentman |first1=D.D. |last2=Fraser |first2=B. J. |date=1991 |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 |issue=9 |pages=15973–15984 |bibcode=1991JGR....9615973S |doi=10.1029/91JA01085}}</ref> 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.<ref name="Pechony Price"/>

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. 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 |last1=Pechony |first1=O. |last2=Price |first2=C. |date=2006 |title=Schumann Resonances: interpretation of local diurnal intensity modulations |journal=Radio Science |volume=42 |issue=2 |pages=RS2S05 |bibcode=2006RaSc...41.2S05P |doi=10.1029/2006RS003455|s2cid=119780816 |doi-access=free }}</ref>

Schumann resonance [[amplitude]] records show significant diurnal and seasonal variations which generally 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 |last1=Yang |first1=H. |last2=Pasko |first2=V. P. |date=2007 |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 |pages=RS2S14 |bibcode=2006RaSc...41.2S14Y |doi=10.1029/2005RS003402|doi-access=free }}</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. 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 non-unique interpretations.

==== "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 because the mean rate of excitation by lightning, ~50 lightning events per second globally, mixes up the individual contributions together.  However, occasionally extremely large lightning flashes occur 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  them to be considered 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.

=== Transient luminous events research ===

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 |last1=Boccippio |first1=D. J. |last2=Williams |first2=E. R. |last3=Heckman |first3=S. J. |last4=Lyons |first4=W. A. |last5=Baker |first5=I. T. |last6=Boldi |first6=R. |display-authors=4 |date=1995 |title=Sprites, ELF transients, and positive ground strokes |journal=Science |volume=269 |issue=5227 |pages=1088–1091 |bibcode=1995Sci...269.1088B |doi=10.1126/science.269.5227.1088 |pmid=17755531|s2cid=8840716 }}</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 |last1=Price |first1=C. |last2=Greenberg |first2=E. |last3=Yair |first3=Y. |last4=Sátori |first4=G. |last5= Bór |first5=J. |last6=Fukunishi |first6=H.  |last7= Sato |first7=M. |last8=Israelevich |first8=P.  |last9= Moalem |first9=M. |display-authors=4 |date=2004 |title=Ground-based detection of TLE-producing intense lightning during the MEIDEX mission on board the Space Shuttle ''Columbia'' |journal=Geophysical Research Letters |volume=31 |issue=20 |page=L20107 |bibcode=2004GeoRL..3120107P |doi=10.1029/2004GL020711 |first10=A. |last10=Devir |first11=Z. |last11=Levin |first12=J. H. |last12=Joseph |first13=I. |last13=Mayo |first14=B. |last14=Ziv |first15=A. |last15=Sternlieb|doi-access=free }}</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 |last1=Hu |first1= W. |last2=Cummer |first2=S. A.  |last3=Lyons |first3=W. A.  |last4=Nelson |first4=T. E.  |date=2002 |title=Lightning charge moment changes for the initiation of sprites |journal=Geophysical Research Letters |volume=29 |issue=8 |page=1279 |bibcode=2002GeoRL..29.1279H |doi=10.1029/2001GL014593|doi-access=free }}</ref>

==== Global temperature ====

Williams [1992]<ref name="Williams 1992">{{Cite journal |last=Williams |first= E.R. |date=1992 |title=The Schumann resonance: a global tropical thermometer |journal=Science |volume=256 |issue=5060 |pages=1184–1186 |bibcode=1992Sci...256.1184W |doi=10.1126/science.256.5060.1184 |pmid=17795213|s2cid= 26708495 }}</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 |last=Williams |first= E.R. |date=1989 |title=The tripole structure of thunderstorms |journal=Journal of Geophysical Research |volume=94 |issue= D11 |pages=13151–13167 |bibcode=1989JGR....9413151W |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. A paper was published in 2006 linking Schumann resonance to [[global surface temperature]],<ref name="M. Sekiguchi M. Hayakawa A. P. Nickolaenko Y. Hobara 2006">{{Cite journal |last1=Sekiguchi |first1=M.  |last2=Hayakawa |first2=M.  |last3=  Nickolaenko |first3=A. P. |last4=Hobara |first4= Y.  |date=2006 |title=Evidence on a link between the intensity of Schumann resonance and global surface temperature |journal=Annales Geophysicae |volume=24 |issue=7  |pages=1809–1817 |bibcode=2006AnGeo..24.1809S |doi=10.5194/angeo-24-1809-2006|doi-access=free }}</ref> which was followed up with a 2009 study.<ref name="Hobara, Y.; Harada, T.; Hayakawa, M.; Sekiguchi, M.; Ohta, K. 2009">{{Cite journal |last1=Hobara |first1=Y. |last2=Harada |first2=T. |last3=Hayakawa |first3=M. |last4=Sekiguchi |first4=M. |last5=Ohta |first5= K. |year=2009 |title=Study on monitoring global warming by using the data of Schumann resonance |journal=AGU Fall Meeting Abstracts |volume=2009 |pages=AE43B–0267 |bibcode=2009AGUFMAE43B0267H}}</ref>

==== 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 effects 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 book |title=Climate Processes and Climate Sensitivity |last1=Hansen |first1=J. |last2= Lacis |first2=A. |last3=Rind |first3=D.  |last4= Russel |first4=G. |last5= Stone |first5=P. |last6= Fung |first6=I. |last7= Ruedy |first7=R. |last8= Lerner |first8=J. |date=1984 |editor-last=Hansen  |editor-first=J. E.  |series=AGU Geophysical Monograph Series |volume=29 |pages=130–163 |chapter=Climate sensitivity: Analysis of feedback mechanisms |bibcode=1984GMS....29..130H |doi=10.1029/gm029p0130 |display-authors=4 |editor-last2=Takahashi |editor-first2=T.|isbn=978-0-87590-404-7 }}</ref> but whether this impact is a positive or a negative [[feedback]] is still uncertain.<ref name="Rind 1998">{{Cite journal |last=Rind |first=D. |date=1998 |title=Just add water vapor |journal=Science |volume=28 |issue=5380 |pages=1152–1153 |doi=10.1126/science.281.5380.1152|s2cid=129504960 |url=https://zenodo.org/record/1231141 }}</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 |last=Price |first=C. |date=2000 |title=Evidence for a link between global lightning activity and upper tropospheric water vapor |journal=Nature |volume=406 |issue=6793 |pages=290–293 |doi=10.1038/35018543 |pmid=10917527|bibcode=2000Natur.406..290P |s2cid=4422715 }}</ref> suggested that changes in the UTWV can be derived from records of Schumann resonances.

== On other planets and moons ==
{{More citations needed|section|date=July 2021}}
The existence of Schumann-like resonances is conditioned primarily by two factors:
# A closed, planetary-sized and ellipsoidial 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.
# A source of electrical excitation of [[electromagnetic waves]] in the extremely low frequency range.
Within the [[Solar System]] there are five candidates for Schumann resonance detection besides the Earth: [[Venus]], [[Mars]], [[Jupiter]], [[Saturn]], and Saturn's biggest moon [[Titan (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. No ''in situ'' capability exists today to validate the results.

=== Venus ===

The strongest evidence for lightning on Venus comes from the electromagnetic waves first 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 |last1=Nickolaenko  |first1=A. P. |last2=Rabinowicz |first2=L. M.  |date=1982 |title=On the possibility of existence of global electromagnetic resonances on the planets of Solar system |journal=Space Research |volume=20 |pages=82–89}}</ref> and Pechony and Price [2004].<ref name="Pechony Price 2004">{{Cite journal |last1=Pechony |first1=O. |last2= Price |first2=C. |date=2004 |title=Schumann resonance parameters calculated with a partially uniform knee model on Earth, Venus, Mars, and Titan |journal=Radio Science |volume=39 |issue=5 |pages=RS5007 |bibcode=2004RaSc...39.5007P |doi=10.1029/2004RS003056|doi-access=free }}</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.

=== Mars ===

<!-- 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.

Detection of lightning activity on Mars has been reported by Ruf et al. [2009].<ref name="Ruf">{{Cite journal |last1=Ruf |first1=C. |last2=Renno |first2=N. O.  |last3=Kok |first3=J. F.  |last4= Bandelier |first4=E. |last5= Sander |first5=M. J. |last6= Gross |first6=S. |last7=Skjerve |first7=L.  |last8=Cantor |first8=B.  |display-authors=4 |date=2009 |title=Emission of Non-thermal Microwave Radiation by a Martian Dust Storm |journal=Geophysical Research Letters |volume=36 |issue=13 |pages=L13202 |bibcode=2009GeoRL..3613202R |doi=10.1029/2009GL038715|hdl=2027.42/94934 |citeseerx=10.1.1.872.939 |s2cid=14707525 |url=https://deepblue.lib.umich.edu/bitstream/2027.42/94934/1/grl26053.pdf }}</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 |last1=Eden |first1= H. F. |last2=Vonnegut |first2=B.  |date=1973 |title=Electrical breakdown caused by dust motion in low-pressure atmospheres: consideration for Mars |journal=Science |volume=180 |issue=4089 |pages=962–963 |bibcode=1973Sci...180..962E |doi=10.1126/science.180.4089.962 |pmid=17735929|s2cid= 38902776 }}</ref> and Renno et al. [2003].<ref name="Renno 2003">{{Cite journal |last1=Renno  |first1=N. O. |last2=Wong |first2=A.  |last3= Atreya |first3=S. K. |last4=de Pater |first4=I.  |last5=Roos-Serote |first5=M.  |date=2003 |title=Electrical discharges and broadband radio emission by Martian dust devils and dust storms |journal=Geophysical Research Letters |volume=30 |issue=22 |page=2140 |bibcode=2003GeoRL..30.2140R |doi=10.1029/2003GL017879|url=https://deepblue.lib.umich.edu/bitstream/2027.42/95558/1/grl17254.pdf |hdl=2027.42/95558 |doi-access=free }}</ref> 

Martian global resonances were modeled by Sukhorukov [1991],<ref name="Sukhorukov 1991">{{Cite journal |last=Sukhorukov  |first=A. I. |date=1991 |title=On the Schumann resonances on Mars |journal=Planet. Space Sci. |volume=39 |issue=12 |pages=1673–1676 |bibcode=1991P&SS...39.1673S |doi=10.1016/0032-0633(91)90028-9}}</ref> Pechony and Price [2004],<ref name="Pechony Price 2004" /> and Molina-Cuberos et al. [2006].<ref name="Molina-Cuberos ">{{Cite journal |last1=Molina-Cuberos  |first1=G. J. |last2= Morente |first2=J. A. |last3= Besser |first3=B. P. |last4= Porti |first4=J. |last5= Lichtenegger |first5=H. |last6= Schwingenschuh |first6=K. |last7= Salinas |first7=A. |last8=Margineda |first8=J.  |display-authors=4 |date=2006 |title=Schumann resonances as a tool to study the lower ionosphere of Mars |journal=Radio Science |volume=41 |issue=1 |pages=RS1003 |bibcode=2006RaSc...41.1003M |doi=10.1029/2004RS003187|doi-access=free }}</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" />

=== Titan ===

It was long ago suggested that lightning discharges may occur on [[Titan (moon)|Titan]],<ref name="Lammer 2001">{{Cite journal |last1=Lammer  |first1=H. |last2=Tokano |first2=T.  |last3=Fischer |first3=G.  |last4= Stumptner |first4=W. |last5=Molina-Cuberos |first5=G. J.  |last6= Schwingenschuh |first6=K. |last7= Rucher |first7=H. O. |display-authors=4 |date=2001 |title=Lightning activity of Titan: can Cassiny/Huygens detect it? |journal=Planetary and Space Science |volume=49 |issue=6 |pages=561–574 |bibcode=2001P&SS...49..561L |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 have received more attention than on any other celestial body, in works by Besser et al. [2002],<ref name="Besser 2002">{{Cite journal |last1=Besser |first1=B. P. |last2=Schwingenschuh |first2=K.  |last3= Jernej |first3=I. |last4= Eichelberger |first4=H. U. |last5= Lichtenegger |first5=H. I. M. |last6= Fulchignoni |first6=M. |last7= Molina-Cuberos |first7=G. J. |last8=Morente |first8=J. A.  |last9=Porti |first9=J. A.  |display-authors=4 |date=2002 |title=Schumann resonances as indicators for lighting on Titan |journal=Proceedings of the Second European Workshop on Exo/Astrobiology, Graz, Austria, September 16–19 |first10=A. |last10=Salinas}}</ref> Morente et al. [2003],<ref name="Morente 2003">{{Cite journal |last1=Morente  |first1=J. A. |last2=Molina-Cuberos  |first2=G. J. |last3=Porti  |first3=J. A. |last4= Schwingenschuh |first4=K. |last5=Besser |first5=B. P.  |display-authors=4 |date=2003 |title=A study of the propagation of electromagnetic waves in Titan's atmosphere with the TLM numerical method |journal=Icarus |volume=162 |issue=2 |pages=374–384 |bibcode=2003Icar..162..374M |doi=10.1016/S0019-1035(03)00025-3}}</ref> Molina-Cuberos et al. [2004],<ref name="Molina-Cuberos 2004">{{Cite journal |last1=Molina-Cuberos  |first1=G. J. |last2= Porti |first2=J. |last3=Besser |first3=B. P.  |last4= Morente |first4=J. A. |last5=Margineda |first5=J.  |last6= Lichtenegger |first6=H. I. M. |last7=Salinas |first7=A.  |last8= Schwingenschuh |first8=K. |last9= Eichelberger |first9=H. U. |display-authors=4 |date=2004 |title=Shumann resonances and electromagnetic transparence in the atmosphere of Titan |journal=Advances in Space Research |volume=33 |issue=12 |pages=2309–2313 |bibcode=2004AdSpR..33.2309M |doi=10.1016/S0273-1177(03)00465-4}}</ref> Nickolaenko et al. [2003],<ref name="Nickolaenko 2003">{{Cite journal |last1=Nickolaenko  |first1=A. P. |last2=Besser |first2=B. P.  |last3= Schwingenschuh |first3=K. |date=2003 |title=Model computations of Schumann resonance on Titan |journal=Planetary and Space Science |volume=51 |issue=13 |pages=853–862 |bibcode=2003P&SS...51..853N |doi=10.1016/S0032-0633(03)00119-3}}</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.

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 a few tens of km of the icy subsurface crust.<ref>{{Cite journal |last1=Béghin |first1=C. |last2=Simões |first2=F. |last3=Krasnoselskikh |first3=V. |last4=Schwingenschuh |first4=K. |last5=Berthelier |first5=J. |last6=Besser |first6=B. |last7=Bettanini |first7=C. |last8=Grard |first8=R. |last9=Hamelin |first9=M. |display-authors=4 |date=November 1, 2007 |title=A Schumann-like resonance on Titan driven by Saturn's magnetosphere possibly revealed by the Huygens Probe |journal=Icarus |volume=191 |issue=1 |pages=251–266 |doi=10.1016/j.icarus.2007.04.005 |first10=J. J. |last10=López-Moreno |first11=G. J. |last11=Molina-Cuberos |first12=T. |last12=Tokanoh |bibcode=2007Icar..191..251B}}</ref><ref>{{Cite journal |last1=Béghin |first1=C. |last2=Canu |first2=P. |last3=Karkoschka |first3=E. |last4=Sotin |first4=C. |last5=Bertucci |first5=C. |last6=Kurth |first6=W.S. |last7=Berthelier |first7=J.J. |last8=Grard |first8=R. |last9=Hamelin |first9=M. |display-authors=4 |date=December 2009 |title=New insights on Titan's plasma-driven Schumann resonance inferred from Huygens and Cassini data |journal=Planetary and Space Science |volume=57 |issue=14–15 |pages=1872–1888 |bibcode=2009P&SS...57.1872B |doi=10.1016/j.pss.2009.04.006|hdl=11336/20677 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Béghin |first1=Christian |last2=Sotin |first2=Christophe |last3=Hamelin |first3=Michel |date=June 2010 |title=Titan's native ocean revealed beneath some 45km of ice by a Schumann-like resonance |journal=Comptes Rendus Geoscience |volume=342 |issue=6 |pages=425–433 |bibcode=2010CRGeo.342..425B |doi=10.1016/j.crte.2010.03.003|url=https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.1016/j.crte.2010.03.003/ }}</ref><ref>{{Cite journal |last1=Béghin |first1=Christian |last2=Randriamboarison |first2=Orélien |last3=Hamelin |first3=Michel |last4=Karkoschka |first4=Erich |last5=Sotin |first5=Christophe |last6=Whitten |first6=Robert C. |last7=Berthelier |first7=Jean-Jacques |last8=Grard |first8=Réjean |last9=Simões |first9=Fernando |display-authors=4 |title=Analytic theory of Titan's Schumann resonance: Constraints on ionospheric conductivity and buried water ocean |journal=Icarus |volume=218 |issue=2 |pages=1028–1042 |doi=10.1016/j.icarus.2012.02.005 |bibcode=2012Icar..218.1028B |year=2012|hdl=2060/20140002248 |s2cid=26341590 |hdl-access=free }}</ref>
<!-- ToDo: verify refs, assign to statements, format, find independent sources -->

=== Jupiter and Saturn ===

Lightning activity has been optically detected on Jupiter. Existence of lightning activity on that planet was predicted by Bar-Nun [1975]<ref name="Bar-Nun">{{Cite journal |last=Bar-Nun  |first=A. |date=1975 |title=Thunderstorms on Jupiter |journal=Icarus |volume=24 |issue=1 |pages=86–94 |bibcode=1975Icar...24...86B |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 (spacecraft)|Cassini]]. Saturn is also confirmed to have [[Saturn Electrostatic Discharges|lightning activity]].<ref>{{Cite web |url=http://www.ciclops.org/view_event/178/Lightning_Flashing_in_Daylight |title=Lightning Flashing in Daylight (Saturn Images from NASA's Cassini Spacecraft) |website=www.ciclops.org |access-date=2017-11-08 |archive-date=September 23, 2015 |archive-url=https://web.archive.org/web/20150923203444/http://www.ciclops.org/view_event/178/Lightning_Flashing_in_Daylight |url-status=dead }}</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.<ref name="Sentman 1990"/>

Little is known about the electrical parameters of the interior of Jupiter or Saturn. 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 |last=Sentman  |first=D. D. |date=1990 |title=Electrical conductivity of Jupiter's Shallow interior and the formation of a resonant planetary-ionosphere cavity |journal=Icarus |volume=88 |issue=1 |pages=73–86 |bibcode=1990Icar...88...73S |doi=10.1016/0019-1035(90)90177-B}}</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.

== See also ==
* [[Cymatics]]
* [[The Hum]]
* [[Plasma (physics)]]
* [[Radiant energy]]
* [[Telluric current]]

== Citations ==
{{Reflist|30em}}

== External articles and references ==
{{Commons category|Schumann resonance}}
'''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]
* Sprite research video: [http://video.pbs.org/video/2365124484/ The A.C. global circuit Schumann resonances oscillate at only eight cycles per second]

'''Websites'''
* [https://www.scribd.com/document/186741298/Construction-and-Deployment-of-an-ULF-Receiver-for-the-Study-of-Schumann-Resonance-in-Iowa "Construction and Deployment of an ULF Receiver for the Study of Schumann Resonance in Iowa"] {{Webarchive|url=https://web.archive.org/web/20230127164611/https://www.scribd.com/document/186741298/Construction-and-Deployment-of-an-ULF-Receiver-for-the-Study-of-Schumann-Resonance-in-Iowa |date=January 27, 2023 }} by Anton Kruger—Well illustrated study from the University of Iowa
* [https://www.heartmath.org/gci/gcms/live-data/spectrogram-calendar/ Global Coherence Initiative (Spectrogram Calendar)] Schumann resonance live data
* [http://sosrff.tsu.ru/?page_id=7 Space Observing System] Schumann resonance live data
* [http://www.earthbreathing.co.uk/index.php/schumann-resonance The Discovery of Schumann Resonance]
* {{Skeptoid | id=4352 | number= 352| title=Facts and Fiction of the Schumann Resonance | date=March 5, 2013 | quote= | access-date=}}

'''Animation'''
* [http://svs.gsfc.nasa.gov/vis/a010000/a010800/a010891/ Schumann resonance animation] {{Webarchive|url=https://web.archive.org/web/20221204220253/https://svs.gsfc.nasa.gov/vis/a010000/a010800/a010891/ |date=December 4, 2022 }} from [[NASA Goddard Space Flight Center]]

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