Systematic deviations in source direction estimates of Q‐bursts recorded at Nagycenk, Hungary

Abstract

Q-bursts are globally detectable extremely low frequency (ELF, 3-3000 Hz) band wave packets produced by intense lightning discharges. Q-bursts recorded in the Széchenyi István Geophysical Observatory (NCK, 16.7°E, 47.6°N), Hungary, on 1 and 2 August 2012 have been analyzed to find azimuths of their sources. The location of parent lightning strokes of 320 and 205 Q-bursts on the 2 days, respectively, have been identified in the records of the World Wide Lightning Location Network (WWLLN) using the detection times at NCK. ELF data-based source azimuths were found to differ systematically from source azimuths obtained from WWLLN lightning locations. The difference between the corresponding azimuth values depends on the azimuth of the source. This variation of the source azimuth error mirrors the symmetry of the conductance of the Earth's crust inferred from magnetotelluric measurements around NCK. After correction for the azimuthal dependence, the variation of the residual error shows a diurnal pattern with positive azimuth deviations occurring near midnight, local time. Füllekrug and Sukhorukov (1999) suggested that the anisotropic conductivity in the Earth's crust below the observatory and the different daytime and nighttime conductivities in the lower ionosphere, respectively, may cause the identified error terms. Our results emphasize the substantial effect of anisotropic conductivity in the Earth's crust around the recording station on the accuracy of ELF direction finding. The need for theoretical approach and more measurements is pointed in understanding the underlying mechanisms quantitatively and in investigating whether ELF observations can be used in geophysical prospecting.

Measurements of atmospheric electricity in the Széchenyi István Geophysical Observatory, Hungary

“…-The analysis of errors in the ELF data-based estimations of source direction of Q bursts detected at the NCK station supports the suggestion that regions of inhomogeneous conductivity in the waveguide boundary regions (also those in the Earth's crust which can affect the measured polarization of transient ELF signals) and source localization can be improved significantly if the corresponding effect is correctly taken into account (Bór et al, 2016).…”

“…Recently, this question has been revisited and preliminary results, based on numerical modelling and on-site PG measurements, confirm that the reduction in PG can be attributed to the shielding effect of the local trees. Using correction factors derived from the numerical model, the shielding effect can be eliminated from the long-term PG datasets (Buzás et al, 2018).…”

The Accuracy of Radio Direction Finding in the Extremely Low Frequency Range

“…However, the accuracy of this procedure is still limited; we did not expect it to be better than about ±1°. Another factor that can influence the angle of arrival inferred from the signal is the local ground conductivity (Bór et al, ). The accuracy of direction finding is also strongly influenced by the Schumann resonance background.…”

“…In this study, we focus on the accuracy of direction finding using one receiver equipped with two orthogonal magnetic antennas (induction coils). In a similar study published recently by Bór et al (2016), the authors analyzed the accuracy of direction finding using their ELF station in Hungary. They identified the local anisotropic ground conductivity as the dominant factor of error.…”

ELF Electromagnetic Waves from Lightning: The Schumann Resonances

“…However, it should be noted that not all sprites produce strong ELF transients [144,145]. Furthermore, recent studies show that due to anisotropic conductivity of the Earth's crust, the determination of the source direction using SR methods can have significant errors [144,146].…”