Correlation between SQUID and Fluxgate Magnetometer Data-sets for Geomagnetic Storms: Hermanus

[摘要] ENGLISH ABSTRACT: Superconducting QUantum Interference Devices (SQUIDs) are fairly recenttypes of magnetometers that use flux quantization combined with Josephsontunnelling to detect very faint (< 10¯15 T) magnetic fields. Recent scientificstudies have shown that these highly sensitive magnetometers, located in anultra-low-noise environment, are capable of observing Earth-ionosphere couplings,such as P waves emitted during earthquakes or magnetic storms inthe upper atmosphere, S and T breathing modes of the Earth during quietmagnetic and seismic periods, signals in time correlating with sprites. SinceSQUIDs are much more sensitive than conventional magnetometers, they arearguably the best tool for understanding space weather and natural hazards,whether they are produced from space or within the ionosphere by magneticstorms for instance, or natural disturbances, including magnetic disturbancesproduced by earthquakes or as a result of the dynamics of the earth's core.A study was conducted at SANSA Space Science in Hermanus, WesternCape, in 2012, to find the correlation between SQUID and Fluxgate data-sets,with the aim of validating the use of a SQUID as a reliable instrument for SpaceWeather observations. In that study, SQUID data obtained from the LowNoise Laboratory (LSBB) in France was compared to Fluxgate data-sets fromthe three closest magnetic observatories to LSBB, namely Chambon la For êt(France), Ebro (Spain) and Fürstenfeldbruck (Germany), all further than 500km from LSBB. As a follow-up study, our aim is to correlate the SANSA SpaceScience SQUID data at Hermanus with Fluxgate magnetic data also recordedon-site (at Hermanus). There are notable di_erences between the previousstudy and the current study. In the previous study, the three-axis SQUIDused comprised of three low-Tc devices operated in liquid helium (4.2 K) in anunderground, low noise environment shielded from most human interferences.The SQUID magnetometer operated at Hermanus for the duration of thisstudy is a high-Tc two-axis device (measuring the x and z components of thegeomagnetic field). This SQUID magnetometer operates in liquid nitrogen(77 K), and is completely unshielded in the local geomagnetic field of about26 uT. The environment is magnetically clean to observatory standards, butexperiences more human interference than that at LSBB. The high-Tc SQUIDsalso experience excessive 1/f noise at low frequencies which the low-Tc SQUIDsdo not suffer from, but the big advantage of the current study is that theSQUIDs are located within 50 m from the observatory's fluxgate. We thusexpect far better correlation between SQUID and fluxgate data than whatwas obtained in the previous study, which should improve the isolation ofsignals detected by the SQUID but not by the fluxgate.

[发布机构] Stellenbosch University