Editing Geophysics (section)

=== Electromagnetic waves ===
[[Electromagnetic waves]] occur in the ionosphere and magnetosphere as well as in [[Earth's outer core]]. [[Dawn chorus (electromagnetic)|Dawn chorus]] is believed to be caused by high-energy electrons that get caught in the [[Van Allen radiation belt]]. [[Whistler (radio)|Whistlers]] are produced by [[lightning]] strikes. [[Hiss (electromagnetic)|Hiss]] may be generated by both. [[Electromagnetic radiation|Electromagnetic]] waves may also be generated by earthquakes (see [[seismo-electromagnetics]]).

In the highly conductive liquid iron of the outer core, magnetic fields are generated by electric currents through electromagnetic induction. [[Alfvén wave]]s are [[magnetohydrodynamic]] waves in the [[magnetosphere]] or the Earth's core. In the core, they probably have little observable effect on the Earth's magnetic field, but slower waves such as magnetic [[Rossby wave]]s may be one source of [[geomagnetic secular variation]].<ref name="Merrill">{{harvnb|Merrill|McElhinny|McFadden|1998}}</ref>

Electromagnetic methods that are used for geophysical survey include [[transient electromagnetics]], [[magnetotellurics]], [[surface nuclear magnetic resonance]] and electromagnetic seabed logging.<ref>{{cite book |last1=Stéphane |first1=Sainson |title=Electromagnetic seabed logging : a new tool for geoscientists |date=2017 |publisher=Springer |isbn=978-3-319-45355-2}}</ref>