Earth's electromagnetic environment

TitleEarth's electromagnetic environment
Publication TypeJournal Article
Year of Publication2016
AuthorsConstable C.
JournalSurveys in Geophysics
Volume37
Pagination27-45
Date Published2016/01
Type of ArticleReview
ISBN Number0169-3298
Accession NumberWOS:000369809700003
Keywordsalgorithm; amt dead band; atmospheric electricity; Audio-magnetotellurics; circuit; Electromagnetism; Geomagnetic spectrum; inversion; ionosphere; Lightning; magnetotellurics; radio transmitters; Schumann resonance; Sferics; sprites; storms
Abstract

The natural spectrum of electromagnetic variations surrounding Earth extends across an enormous frequency range and is controlled by diverse physical processes. Electromagnetic (EM) induction studies make use of external field variations with frequencies ranging from the solar cycle which has been used for geomagnetic depth sounding through the 10-10 Hz frequency band widely used for magnetotelluric and audio-magnetotelluric studies. Above 10 Hz, the EM spectrum is dominated by man-made signals. This review emphasizes electromagnetic sources at 1 Hz and higher, describing major differences in physical origin and structure of short- and long-period signals. The essential role of Earth's internal magnetic field in defining the magnetosphere through its interactions with the solar wind and interplanetary magnetic field is briefly outlined. At its lower boundary, the magnetosphere is engaged in two-way interactions with the underlying ionosphere and neutral atmosphere. Extremely low-frequency (3 Hz-3 kHz) electromagnetic signals are generated in the form of sferics, lightning, and whistlers which can extend to frequencies as high as the VLF range (3-30 kHz).The roughly spherical dielectric cavity bounded by the ground and the ionosphere produces the Schumann resonance at around 8 Hz and its harmonics. A transverse resonance also occurs at 1.7-2.0 kHz arising from reflection off the variable height lower boundary of the ionosphere and exhibiting line splitting due to three-dimensional structure. Ground and satellite observations are discussed in the light of their contributions to understanding the global electric circuit and for EM induction studies.

DOI10.1007/s10712-015-9351-1
Short TitleSurv. Geophys.
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