The contribution of anisotropic conductivity in the ionosphere to lightning flash bearing deviations in the ELF/ULF range

Lightning flash bearing deviations in the ELF/ULF range are monitored at two independently operating measurement instruments in Hollister, California, and Silberborn, Germany. The lightning flash bearing deviation at Hollister exhibits a rotational dependence ∼12°, associated with the conductivity contrast between the Earth's crust and the nearby Pacific Ocean. The bearing deviations at both stations exhibit a pronounced diurnal local time variation ∼11°. This diurnal variation is attributed to the anisotropic conductivity in the ionosphere during day‐ and nighttime conditions. No bearing deviation dependency from the source‐receiver distance can be distinguished. Correction for the mean rotational dependence at Hollister and the mean diurnal variation at both locations results in residual bearing deviations ∼ ±10° which are related to the variability of anisotropic conductivity in the ionosphere on a subdiurnal time scale.