About the world wide magnetic background noise in the millihertz frequency range

Description

In the millihertz range, a single magnetometer can detect magnetic waves in the near-field regime. For such long wavelengths, it can measure the world-wide magnetic-background noise due to any charge displacement on Earth and within its environment. In this frequency band, the normal modes of the Earth's free oscillations exist and when excited, they shake the air column above them, up to the ionosphere where the moving charges emit a magnetic fluctuation, via Ampère's law. We show the magnetic-background noise spectrum obtained by an FFT analysis of 72 consecutive hours of magnetic-seismic calm. It is mostly due to vertical charge oscillations. Even in the absence of a quake larger than Mw= 5.2, spherical and toroidal modes are deected. Instrumental and analytical perspectives are discussed.

Abstract

Europhysics Letters, vol. 88, n°1, pp. 19002, 2009

Abstract

International audience

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