SUBMICROSECOND CHARACTERISTICS OF LIGHTNING RETURN-STROKE CURRENTS

Seventy-four simultaneous submicrosecond time-resolved measurements of triggered return-stroke current (I) and current derivative (dI/dt) were made in Florida in 1987 and 1988. Peak currents ranged from about 5 to 76 kA, peak dI/dt amplitude from 13 to 411 kA/mu-s and rise time from 90 to 1000 ns. The mean peak dI/dt values 110 kA/mu-s are 2-3 times higher than data from instrumented towers and peak I and dI/dt appear to be positively correlated. These data confirm previous experiments (1985, Florida and 1986, France) and conclusions supported by forty measurements. They are important in order to define, for example, standards for lightning protection. Present standards give a dI/dt maximum of 140 kA/mu-s.