Abstract:
The temporal characteristics are analysed of preliminary breakdown pulse trains of
both negative and positive ground flashes, chaotic pulse trains that are associated
with negative subsequent strokes and isolated cloud flashes. The relative strength
(with respect to the succeeding return strokes) of preliminary breakdown pulse trains
of negative return strokes are compared between a data set obtained in Sri Lanka and
that in Sweden. The absolute pulse amplitudes are given for a sample of isolated
cloud flashes distance ranged by time to thunder measurements. The leader fields, the
total leader field change and the ratio of the total leader field change to that of the
return strokes are calculated for channels of which an upper segment is inclined
towards horizontal direction. A large number of return stroke models are reviewed
under their concepts. The widely used engineering type models are generalised by
two sets of equations. The suitability and limitations of the return stroke validation
methods are also discussed. A brief review is given on the analytical expressions
which can be applied to estimate channel base currents once the measured field
parameters are fed as the input. A recently proposed return stroke model was
validated with triggered lightning data by employing a statistical approach. The long
impulse currents of positive return strokes are estimated by feeding measured long
distance fields in to a recently proposed positive return stroke model and also taking
into account the physics of the propagation of ELF sferics in the earth-ionosphere
waveguide, The results are extended to describe some observations pertinent to Red
Sprites and Elves. Laboratory experiments were conducted to investigate the relations
between the optical and current signatures of long sparks. Consequently, the
applicability of the results to deduce lightning parameters were discussed.
