The Electromagnetic Radiation from Lightning in the Interval of 10 Khz to 100 Mhz

Average amplitude spectra are presented for large radiation impulses from the initial stage of 15 cloud-to-ground (CG) and 36 intracloud (IC) lightning discharges. The spectra are obtained by Fourier transformation of the time domain records of lightning radiation fields with wide bandwidth devices. The field records include the electric field change ∆E (bandwidth 0 –500 kHz), the electric field time-derivative dE/dt (bandwidth 0.01–150 MHz), and the magnetic field time-derivative dB/dt (bandwidth 0.01–63.7 MHz). Results show that the initial stage of both the CG and IC lightning discharges produces nearly identical spectra between 0.01 to 100 MHz, which show a decrease proportional to 1/(frequency) in general with a small peak around 60 MHz. The small peak around 60 MHz may be a unique feature associated with the initial breakdown process within clouds.