  The electromagnetic fields associated with tortuous lightning channels are
usually characterised by a pronounced fine structure. This work investigates
and quantifies the effects of channel tortuosity on the return stroke
electromagnetic field shapes in the close lightning environment (the range up
to 100m from the lightning striking point). General equations for lightning
return stroke electromagnetic fields for arbitrarily located observation points
are derived from Maxwell's equations. In order to include arbitrary channel
shapes, the channel is described by a parametric representation in Cartesian
coordinates with the channel length as the free parameter. The return stroke
current required for the evaluation of the derived equations is calculated from
a current generation type model. The field computations show that amplitudes
and waveforms of the electromagnetic fields in the close lightning environment
are considerably influenced by the channel shape. In particular, the induction
component of the electric fields radiated by a tortuous lightning channel
differs significantly from that associated with a straight channel.
