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

Abstract

AbstractQ‐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.