A simplified “engineering” return stroke model

A simplified dipole version for an “engineering” return stroke model is considered. The quantitative estimations of its applicability and possible ways of equivalent dipole moment (or its derivatives) reconstruction are discussed. The model is supplemented with clustered sets of sferic wave forms in very low frequency (VLF) band (0,3...30 kHz). Being registered in hard distance constraints these wave forms can be considered as second derivatives of dipole moments. Their averaged wave forms given as tables or approximations can be used for routine numerical field calculations in different applications.