An axisymmetrical electrostatic model of charges in a thunderstorm clo
ud at the mature stage is used to initiate a bidirectional vertical le
ader that develops into either a cloud-to-ground or an intracloud flas
h from the regions of maximum electric field. The principal result of
this study is the determination of the physical and quantitative relat
ionships among cloud charges, potentials, and electric fields, and the
induced charges, currents, and electric field changes of the lightnin
g channel from the numerical solution of the Poisson equation for a cl
oud charge model with lightning. An important consequence of the model
is that the upper part of the cloud-to-ground leader and the lower pa
rt of the intracloud leader terminate inside the cloud.