Unlike the laws of the propagation of the field, why the shape of Electromagnetic field radiated by lightning increases and take an ascending form far distance?
Dear Djalel Dib, I suggest you read my publication of the IEEE-EMC. The paper shows analyzes that can answer your question and help you in your researches. Sincerely. https://www.researchgate.net/publication/264387155_On_the_Influence_of_Stroke_Current_Propagation_Velocity_on_Lightning_Horizontal_Electric_Fields?ev=prf_pub
Article On the Influence of Stroke Current Propagation Velocity on L...