Distant Electric Fields from Lightning Return Strokes: Influence of Soil Stratification and Frequency-Dependent Parameters

We present an analysis of lightning electric fields taking into account the soil stratification and frequency dependence of its electrical parameters. Two current waveforms corresponding to typical first and subsequent return strokes are considered for the analysis. Different cases for the soil (homogeneous, 2-layer, frequency-dependent/constant electrical parameters) are considered. The simulation results show that the electric field is affected more markedly by the soil stratification than by the frequency dependence of its electrical parameters. Furthermore, subsequent return stroke fields are more significantly affected by the soil stratification and frequency-dependence, compared to first return stroke fields. We present also a comparison between simulation results with simultaneous measurements of current and distant electric fields associated with rocket-triggered lightning flashes. It is shown that the computed electric field waveform for the case of a two-layer soil follows to a much better extent the corresponding experimental wavefroms. The frequency-dependence of the soil affects slightly the early-time response of the field. However, the late-time response of the field is essentially determined by the soil stratification.