Simplified Expressions of Cloud Lightning Electromagnetic Fields Produced by Vertical Channel

In order to meet the actual demand of cloud lightning channel current inversion, a theoretical calculation model of lightning electromagnetic fields produced by vertical cloud lightning channel is established based on the dipole method, and the simplified relationship between the cloud lightning electromagnetic field at ground level from the vertical channel and the channel current is presented. By comparing the cloud lightning electromagnetic fields from the simplified expressions with that from the exact expressions, the influences of the observation distance, the channel length and the channel starting height on the accuracy of the simplified expressions are obtained, and the application ranges of the simplified expressions are also given.