Polarisation properties of [SQUID]² horizontal components at the LSBB (Laboratoire Souterrain à Bas Bruit)

Department of Physics, College of Science and Technology, University of Rwanda, Rwanda

^a e-mail: kwistiand@gmail.com

Abstract

Polarisation properties of the geomagnetic signal are computed using the coherence matrix of horizontal components (EW and NS) of the [SQUID]² datasets, in a relatively small bandwidth. Wavefront ellipticity, signal-to-noise ratio (snr) and wavefront arrival angle of the magnetic quasi-monochromatic waves are determined. From the variation of ellipticity extremum position in the vicinity of 8 Hz, the temporal variation of the peak frequency is traced for the LSBB and two Northern American stations distant from the LSBB by ∼8,000 km. The spectra of the peak frequency variation display the daily, half daily and third-daily harmonics at all stations, which are characteristic of the first Schumann resonance. Ellipticity spectrograms also unveil a type of chirping local nighttime resonances, known as ionospheric Alfvén resonances (IAR), observed at all stations. Thanks to the snr spectrograms, components of the signal which are local to the LSBB station are cancelled from the output, particularly the 50-Hz power grid signal which is minimised in the snr spectra.