资源环境科技发展态势分析平台

The statistical distribution of peak currents in cloud-to-ground lightning strokes is analyzed and discussed both in the context of the existing experimental data and from a theoretical viewpoint. The distributions of peak currents directly measured at instrumented towers are compared to those of peak currents reported by the U.S. National Lightning Detection Network and peak currents measured in rocket-triggered lightning experiments; all those appear to be lognormal. To explain the observed peak current distributions, a simple model based on the large-scale electric field evolution prior to lightning flashes is developed. Based only on the most general assumptions concerning the probability of occurrence of lightning discharge, it is shown that the distribution of the pre-first-stroke large-scale electric field is close to lognormal in a certain range. With the introduction of structure factors relating the leader or cloud electric potential to this field, semiempirical relationships between the potential and the peak current in negative first and subsequent strokes imply that the peak current and pre-first-stroke large-scale electric field obey distributions of the same type. It is demonstrated that with a suitable choice of parameters, the model-predicted distributions are close to those obtained from direct measurements, and statistical tests show that their agreement with the data is at least as good as that seen for lognormal approximations.