In order to deduce the form of the current pulse in a lightning return stroke at altitude from measurements made at ground level, a model of the channel is required. Inductance and capacitance values for a ladder LCR network representing the lightning channel are deduced from the initial electrostatic field distribution around a simplified model of a charged cloud and a vertical unbranched leader. The resistance of the channel is assumed constant with height, and all the network parameters are assumed independent of time. Current pulses are calculated at ground level and at various heights. The pulse parameters deduced at ground level are in rough agreement with observation. The predicted variation of the current pulse with altitude is discussed, and the implications for assessing the risks to aircraft are briefly described.

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