Geophysical signals in the 3-50 Hz ELF band

The British Geological Survey have been operating two high-frequency induction coil magnetometers (100 Hz cadence) at their observatory in Eskdalemuir (Scottish Borders) [54.3°N; 3.2°W] since Jun 2012. They have an approximate sensitivity of 0.07 pTat 0.1—50 Hz. The geophysical signals within the dataset encompass the Schumann Resonances (SR) generated by energy from equatorial lightning refracting in the Earth-ionosphere cavity [Ref. 1], the Ionospheric Alfvén Resonances (IAR) of the upper ionosphere cavity and magnetospheric pulsations (0.001-10 Hz) triggered by geomagnetic storms. We can also observe several subharmonics of the UK 50 Hz power grid. On occasion, local lightning strikes can also be observed directly in the data. These signals range in amplitude from 0.5 pT for the IAR to 5 pT for the SR and over 250 pTfor lightning strikes. In this poster, we give examples of spectrograms showing each type of geophysical signal and describe their occurrence statistics and typical amplitude ranges.