Electromagnetic Fields of Lightning Return Strokes-Revisited

Electric and/or magnetic fields are generated by stationary charges, uniformly moving charges and accelerating charges. These field components are described in the literature as static fields, velocity fields (or generalized Coulomb field) and radiation fields (or acceleration fields), respectively. In the literature, the electromagnetic fields generated by lightning return strokes are presented using the field components associated with short dipoles and in this description the one to one association of the electromagnetic field terms with the physical process that gives rise to them is lost. In this paper, we will derive expressions for the electromagnetic fields using field equations associated with accelerating (and moving) charges and separate the resulting fields into static, velocity and radiation fields. The results illustrates how the radiation fields emanating from the lightning channel give rise to field terms varying as inverse of distance and distance squired, the velocity fields generating field terms varying as inverse of distance squired and the static fields generating fields components varying as inverse of distance squired and distance cube. These field components depend explicitly on the speed of propagation of the current pulse. However, the total field does not depend explicitly on the speed of propagation of the current pulse. It is shown that these field components can be combined to generate the field components pertinent to the dipole technique. However, in this conversion process the connection of the field components to the physical process taking place at the source that generate these fields (i.e. static charges, uniformly moving charges and accelerating charges) is lost.