The electric fields produced by lightning stepped leaders

The electric fields produced by stepped and dart-stepped leaders which immediately precede return strokes in lightning discharges to ground have been recorded in Florida and Arizona. The mean interval time between normal steps is about 16 μs, and the mean interval between dart steps is 6–8 μs. The amplitudes of leader pulses in Florida increase just prior to the return stroke, the largest usually being about 10% of the return stroke peak. In Arizona the leader pulse amplitudes are smaller than those in Florida, in relation to the return stroke, and are not as easy to identify. The shapes of the fields produced by normal steps are similar to dart steps, and the dart steps are very similar to regular sequences of pulses produced by many intracloud discharges. The 10–90% rise times of individual step wave forms are often less than 0.3 μs, and the full width at half maximum of a step pulse is typically 0.4–0.5 μs under conditions where the propagation distortion is minimal. The amplitudes and the shapes of leader step wave forms suggest that the peak step current is at least 2000–8000 A close to the ground and that the maximum rate of change of step current is 6–24 kA/μs or larger. A rough estimate of the minimum charge lowered during the formation of a step is (1–4) × 10−3 C.

[1]  Martin A. Uman,et al.  Test of the Principle of Operation of a Wideband Magnetic Direction Finder for Lightning Return Strokes , 1976 .

[2]  Martin A. Uman,et al.  Electric field statistics for close lightning return strokes near Gainesville, Florida , 1976 .

[3]  James R. Wait.  Transient Fields of a Vertical Dipole Over a Homogeneous Curved Ground , 1956 .

[4]  Martin A. Uman,et al.  Electric field intensity of the lightning return stroke , 1973 .

[5]  E. Philip Krider,et al.  Regular radiation field pulses produced by intracloud lightning discharges , 1975 .

[6]  M. Uman,et al.  The electromagnetic radiation from a finite antenna , 1975 .

[7]  Martin A. Uman,et al.  Lightning return stroke current from magnetic and radiation field measurements , 1970 .

[8]  E. Philip Krider,et al.  The fine structure of lightning return stroke wave forms , 1978 .

[9]  Richard E. Orville,et al.  Return stroke velocity measurements in multistroke lightning flashes , 1976 .

[10]  E. Philip Krider,et al.  Radiation field wave forms produced by lightning stepped leaders , 1975 .

[11]  Martin A. Uman,et al.  A Gated, Wideband Magnetic Direction Finder for Lightning Return Strokes , 1976 .

[12]  K. Berger,et al.  Novel observations on lightning discharges: Results of research on Mount San Salvatore , 1967 .

[13]  The transient behavior of the electromagnetic ground wave on a spherical earth , 1957 .

[14]  D. J. Malan,et al.  Preliminary discharge processes in lightning flashes to ground , 1957 .

[15]  Martin A. Uman,et al.  Currents in Florida lightning return strokes , 1973 .

[16]  M. Uman,et al.  Exact expression and moment approximation for the electric field intensity of the lightning return stroke , 1971 .

[17]  Martin A. Uman,et al.  Effects of 200 km propagation on Florida lightning return stroke electric fields , 1976 .

[18]  M. Uman,et al.  Magnetic field of lightning return stroke , 1969 .

[19]  S. Moreland.  The Lightning Discharge , 1890, Nature.

[20]  M. Uman,et al.  Radiation field and current of the lightning stepped leader , 1970 .

[21]  E. Krider,et al.  Broadband antenna systems for lightning magnetic fields , 1975 .

[22]  Martin A. Uman,et al.  Correlated electric and magnetic fields from lightning return strokes , 1975 .