Model of the First Lightning Return Stroke Using Bidirectional Leader Concept

We have developed a new lightning return stroke model which takes into account a realistic charge distribution to compute the ambient electric potential. It contains a nonlinear resistance model for the development of the finite conductivity of the lightning channel. It also describes a redistribution of charges after the bottom end of the channel is attached to the potential of the ground. The model is based on solving Maxwell's equations linked to Poisson's equation, and coupled with Ohm's law. The waveshape of the current at the channel base is obtained from the model. The simulated current decreases and its rise time increases with height, which is in accordance with the luminosity observations. The electric and magnetic field waveforms modeled for different distances from the lightning flash show that most of the waveform features typically observed at these distances are well reproduced. We also successfully compare modeled magnetic field waveforms with measurements at the distances larger than 30 km. Plain Language Summary The first return stroke process initiates when a lightning channel connects to the ground and the potential wave propagates upward. We have developed a new model of this process taking into account electrodynamic considerations. As an input for our model, we use a realistic thundercloud charge structure. We infer linear charge densities and potential distributions along the lightning core. As a result of our model, we obtain current waveforms at the base of the lightning channel and waveforms of electromagnetic waves originating from the discharge. We succeed to model basic features of magnetic field waveforms measured by a shielded loop antenna at distances larger than 30 km from the source lightning. We also obtain similar peak currents from our model, as those estimated from independent measurements. Finally, we successfully model the development of the shape of the magnetic and electric field waveforms as a function of the distance from the source lightning discharge. Key Points New electromagnetic return stroke model has been developed Simulated magnetic field waveforms agree well with observations Current waveforms, potential distributions, and linear charge densities have been modeled