A multipole expansion for the EM fields of a linear radiator

It is shown explicitly that the electromagnetic fields of a vertical lightning stroke may be represented as the contribution from a multipole expansion. The first term corresponds to the dipole and the fields have the usual form. Succeeding terms can be important when the height of the stroke is not small compared with the distance to the observer located on the Earth's surface. Both frequency- and time-domain solutions are discussed.<
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