SQUID geomagnetic signal analysis and modelling of Schumann Resonances in the earth-ionosphere cavity

Due to its extreme sensitivity to magnetic flux, vast dynamic range and wide bandwidth, the Superconductive Quantum Interference Device (SQUID) is at the frontier of all existing magnetic field sensors. The direct current SQUID principle is based on quantised flux induced current tunnelling across weak link barriers embedded in a superconductive ring. The SQUID can sense a field of the order of 10−15 T, in the same range as the neuron-cell magnetic activity and operates from quasi-dc to the GHz range. The extreme versatility of the SQUID technology makes it an instrument of choice in state-of-the-art applications including monitoring the Earth’s magnetic field. The geomagnetic field is by far one of the most complex systems, as it encompasses field generation phenomena inside the Earth, and the extension of the field into the near-Earth environment, where interaction of ions from the Sun, solar magnetic field and Earth’s magnetic field create a highly dynamic plasma system controlled by the magnetic field. The currents generated in the geomagnetic system induce a magnetic field to the Earth, which are measured in the Ultra Low Frequency (ULF [3×10−3−3] Hz) domain. Between the solid Earth and the layer of ionised gases in the atmosphere, a natural potential difference builds up. Breakdown occurs in forms of short-lived intense channels of current between the Earth and the cloud and beyond: Lightning. There is approximately fifty lightning flashes from approximately a thousand active thunderstorms worldwide every second. From this random generation process emanates electromagnetic radiation that propagates around the Earth, and interferes to form a permanent background noise in the Extremely Low Frequency (ELF [3−3000] Hz), where it forms spectra of highly damped resonances observable in the frequency range 0− 100 Hz, the Schumann resonances. In quiet magnetospheric conditions, Schumann resonances behave as transverse magnetic components, where the electric field is radial and magnetic field is tangential to the Earth’s surface. The Schumann resonances’ intensity is associated with the thunderstorm sources. The interdependence between tropical temperature and thunderstorm generation processes has led to an investigation of the link between global warming and the intensity of the first Schumann resonance. A connection between Schumann resonance disturbances and anomalies in the ionosphere and prior to strong earthquakes has also been observed. Therefore, monitoring the Earth’s magnetic field for natural disaster mitigation has been one of the main priorities of the SQUID network established in partnership between France and South Africa. This project correlates the SQUID response of two SQUIDs installed at Laboratoire Souterrain à Bas bruit in Rustrel, France and at the Space Science directorate of the South African National Space Agency (SANSA) located in Hermanus, South Africa. In this project, along with data spectral analysis, a Finite-Difference Time-Domain (FDTD) based simulation of the entire Earth-Ionosphere system is done using commercially available software: CST Microwave Studio. Stellenbosch University https://scholar.sun.ac.za