Directivity of radiation of lightning discharges

The expressions are given and the properties of the directivity of electromagnetic waves (horizontal component H φ of the magnetic field intensity) excited by high-current components of the lightning flashes (main impacts) are analyzed. The given component is expressed in quadratures for the arbitrary form of current and speed of motion of its front. Analysis is performed for models that emphasize various features of spatial-temporal structure of the radiator and, in particular, for a traveling pulse of current that has a fixed form and whose spatial distribution along the channel depends on time. The results of calculations of the considered field component and its spatial-temporal localization obtained for different approximations of current and speed with the parameters corresponding to backward impacts are discussed.