Initial breakdown and fast leaders in lightning discharges producing long‐lasting disturbances of the lower ionosphere

Abstract

The recent discovery of long recovery, early VLF scattering events (LOREs) indicates that the electric field changes from lightning discharges are capable of producing long‐lasting disturbances (up to tens of minutes) in the upper mesosphere and lower ionosphere. Comparison of lightning mapping array, broadband (up to 10 MHz) electric field, and VLF (∼300 Hz to 42 kHz) magnetic field measurements shows that the field changes produced by initial breakdown (IB) processes and the following leaders in natural, cloud‐to‐ground lightning discharges are detectable in VLF magnetic field measurements at long distances. IB radiation has been detected in VLF for lightning discharges occurring up to 2630 km away from the VLF observing station. Radio atmospherics associated with 52 LOREs, 51 regular recovery events, and 3098 flashes detected by National Lightning Detection Network and/or GLD360 were examined for IB radiation occurring up to 15 ms before the return stroke. Our analysis reveals that in contrast to regular recovery early VLF events, LOREs are strongly associated with lightning discharges which exhibit an intense IB process and a fast first leader (typical duration <4 ms). These experimental results demonstrate that initial breakdown and leader processes are indicators of discharge properties highly relevant to the total energy transfer between lightning discharges and the middle/upper atmosphere.

A model of preliminary breakdown pulse peak currents and their relation to the observed electric field pulses

“…Modeled PBP pulses have characteristic speeds of the step formation of the order 10 7 m/s, which is around 1 order of magnitude larger than the leader effective propagation speeds estimated experimentally by Kolmašová et al [] and by Kotovsky et al []. These estimates, however, also include pauses between individual steps.…”

Initial Breakdown Pulses Accompanied by VHF Pulses During Negative Cloud‐to‐Ground Lightning Flashes

“…IB pulses are thought to be generated by currents flowing in the intermittently extending in‐cloud lightning leaders (Stolzenburg et al, ). The IB pulses can be detected hundreds of kilometers from the parent thunderstorm (Kolmašová et al, ; Kotovsky et al, ) and are one indication of lightning initiation. Another indication of lightning initiation is an initial E‐change (IEC) that occurs immediately before the first IB pulse and can be detected only at short distances (typically within 7 km) from the developing discharge (Chapman et al, ; Marshall, Stolzenburg, et al, ; Marshall et al, ).…”

Lightning initiation: Strong pulses of VHF radiation accompany preliminary breakdown

“…Several other studies 22 – 25 used an LMA system of eight stations operating at 66–72 MHz in Florida, US with a capability to locate a VHF radiation source every 10 μs. Descending VHF radiation sources were observed during the initial breakdown stage of a negative cloud-to-ground flashe 23 but the association of these VHF sources to individual PB pulses was not discussed. Initial breakdown periods of other analyzed flashes (8 cloud-to-ground and 7 intracloud flashes) 24 always contained several geo-located VHF radiation sources which occurred unrelated to PB pulses, supporting thus the previously discussed absence of coincidence between the two phenomena.…”