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Keywords:

  • atmospheric electricity;
  • atmospheric electromagnetics;
  • scaling law

The electromagnetic environment surrounding Earth, including the geomagnetic field and atmospheric electric fields, varies on all time scales, but this frequency dependence has not been well studied. Analyzing observations compiled from several published sources,Füllekrug and Fraser-Smith found that the energy density of the electromagnetic fields at the surface of the Earth follows a simple, fundamental scaling law: The energy density of the fields at a given frequency is inversely proportional to the square of the frequency. This relationship extends over a wide range of frequencies—16 orders of magnitude. The authors note that this is somewhat surprising, given the many different processes that cause electromagnetic field variations, including lightning discharge in the atmosphere, geomagnetic storms in the ionosphere, and many other electromagnetic effects, such as sprites in the middle atmosphere.