On the relationship between lightning peak current and Early VLF perturbations

Lightning strokes are known to cause direct heating and ionization of the D region, some of which are detected via scattering of VLF transmitter signals and are known as Early VLF events. The disturbed ionosphere typically recovers in many tens of seconds. New experimental evidence is presented demonstrating that the scattering pattern and onset amplitude of Early VLF events are strongly related to both the magnitude and polarity of causative lightning peak current. Observations of Early VLF events at nine Stanford VLF receiver sites across the continental United States are combined with lightning geolocation data from the National Lightning Detection Network (NLDN). During January and March 2011, NLDN recorded 7769 intense lightning discharges with high peak currents (>100 kA) generating 1250 detected Early VLF events. We show that the size of the scattered field due to the ionospheric disturbance increases with the peak current intensity of the causative lightning discharge. The most intense peak currents of >+200 and