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

Kwisanga, Christian (2016-03)

Thesis (D.Phil)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: 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 10ˉ¹⁵ 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 x 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.

AFRIKAANSE OPSOMMING: Die Supergeleidende Kwantum Interferensietoestel (SQUID) is op die voorfront van alle bestaande magneetveldsensors, omdat dit uiters sensitief is vir magnetiese vloed en ‘n bree meetbereik het. Die gelykstroom SQUID is gebasseer op die beginsel dat kwantifiseerde vloed stroom indusseer wat tonnel deur swak-kontak versperrings binne ‘n supergeleidende ring. Die SQUID kan veld tot die orde van 10ˉ¹⁵ T waarneem, wat in dieselfde orde is as neuronaktiwiteit en funksioneer vanaf kwasi-gelykstroom tot THz frekwensies. Die uiterste veelsydigheid van die meettegniek maak die SQUID ‘n instrument van keuse in die voorste toepassings, insluitend die monitering van die Aarde se magneetveld. Die Aarde se magneetveld is ‘n baie komplekse stelsel, omdat dit veld-opwekkingsverskynsels binne die Aarde, asook die pad van die veld in die naby-aarde omgewing behels. Interaksie tussen ione van die Son, Son se magneetveld en Aarde se magneetveld skep ‘n hoogs dinamiese ioniese gassisteem wat deur die magneetveld beheer word. Die strome wat in die geomagnetiese stelsel genereer word indusseer ‘n magneetveld tot die Aarde, wat in die ultra-lae frekwensiegebied (ULF [3x10⁻³ -3] Hz) gemeet word. ‘n Potensiaalverskil word opgebou tussen die soliede Aarde en die laag van ioniese gasse in die atmosfeer. Afbreking vind plaas deur middle van ‘n kort, intense stroom tussen wolke en die Aarde en so meer: weerlig. Daar is na beraming vyftig weerligflitse van ongeveer ‘n duisend aktiewe donderstorms per sekonde wêreldwyd. Vanuit hierdie toevals-opwekkingproses word elektromagnetiese bestraling uitgestraal wat rondom die Aarde propageer, en interferensie veroorsaak wat ‘n permanente agtergrondruis in die ekstreemlaagfrekwensie band (ELF [3-3000] Hz) skep en ‘n spektrum van hoogs gedempte resonansies skep wat waargeneem kan word in die 0 - 100 Hz frekwensieband – die Schumann-resonansies. In ‘n stil magnetosfeer toestand kom die Schumann-resonansies voor soos transversale magneetveldkomponente, waar die elektriese veld radiaal is en magneetveld tangent is. Die intensiteit van Schumannresonansies word assosieer met die bronne van die donderstorms. Die verbinding tussen tropiese temperature en opwekkingsprosesse van donderstorms het gelei tot ‘n ondersoek in die afhanklikheid tussen aardverwarming en die intensiteit van die eerste Schumann-resonansie. ‘n Verband met steurnisse in Schumann-resonansies is ook vasgestel. Dit is ook waargeneem dat anomaliteite in die ionosfeer Schumann-resonansies beïnvloed. Die verligting van natuurrampe deur monitering van die Aarde se magneetveld is ‘n hoofprioriteit van die SQUID-netwerk wat gevestig is in die samewerking tussen Frankryk en Suid-Afrika. Die projek korreleer die SQUID-respons van twee SQUIDs, wat installer is by Laboratoire Souterrain à Bas bruit in Frankryk en by die Ruimtewetenskap Direktoraat van die Suid-Afrikaanse Nasionale Ruimteagentskap (SANSA). Spektrale analise van data is gedoen asook Eindige-Verskil Tydgebied (FDTD) basseerde simulasie van die Aarde-ionosfeerstelsel as geheel, met behulp van ‘n kommersieëlbeskikbare sagtewarepakket: CST Microwave Studio.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98597
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