Effects of Conductivity Perturbations in Time Dependent Global Electric Circuit Model

This study contributes to the understanding of influence of the conductivity perturbations on the ionospheric potential in Earth's global electric circuit (GEC). The conductivity perturbations appearing in middle atmosphere produced by γ-ray bursts from magnetars are studied first. The transient response of the ionospheric potential is modeled in this case and timescales of interest are identified (0.01-10 s). In this case modification of ionospheric potential is small. Additionally, the principal effects of topography and reduction of the conductivity inside the thundercloud are studied. Both of these factors effectively increase the ionospheric potential for a classic source in the GEC represented by a current dipole leading to formation of two main charge centers of the thunderstorm. On the other hand for GEC including topography and conductivity reduction in thunderclouds the contribution of sequence of negative cloud-to-ground lightning discharges to the ionospheric potential is decreased. Simulation results show very good agreement with a simplified approach based on circuit models for conductivity perturbations with horizontal dimensions exceeding 20 km.