Radio emission from negative lightning leader steps reveals inner meter-scale structure

TL;DR

This study uses LOFAR to analyze negative lightning leader steps, revealing streamer formation during corona flashes and providing new insights into lightning dynamics and structure at meter scales.

Contribution

It presents the first observation of streamer formation during natural lightning leader steps using VHF radiation, linking it to corona flashes and advancing lightning physics understanding.

Findings

Multiple VHF pulses emitted during each leader step.

Streamer formation observed during corona flashes.

Stepping length similar to ground observations, but with longer stepping time.

Abstract

We use the Low Frequency ARray (LOFAR) to probe the dynamics of the stepping process of negatively-charged plasma channels (negative leaders) in a lightning discharge. We observe that at each step of a leader, multiple pulses of VHF (30~--~80 MHz) radiation are emitted in short-duration bursts ($<10\ \mu$s). This is evidence for streamer formation during corona flashes that occur with each leader step, which has not been observed before in natural lightning and it could help explain X-ray emission from lightning leaders, as X-rays from laboratory leaders tend to be associated with corona flashes. Surprisingly we find that the stepping length is very similar to what was observed near the ground, however with a stepping time that is considerably larger, which as yet is not understood. These results will help to improve lightning propagation models, and eventually lightning protection models.