Passage I

Negative cloud-to-ground (-CG) and positive cloud-to-ground (+CG) lightning strokes move negative charges and positive charges, respectively, from a cloud to the ground during a thunderstorm. Typically, +CG strokes are less numerous than -CG strokes. Figure 1 shows the number of -CG strokes and the number of +CG strokes during each 5 min of a 3 hr period during a thunderstorm that produced a tornado. Also shown are the time of tornado formation (TF) and the time of tornado dissipation (TD). Table 1 shows the average current and the average duration of the strokes during each 30 min period of the 3 hr.