Spontaneous emergence of space stems ahead of negative leaders in lightning and long sparks

Abstract

We investigate the emergence of space stems ahead of negative leaders. These are luminous spots that appear ahead of an advancing leader mediating the leader's stepped propagation. We show that space stems start as regions of locally depleted conductivity that form in the streamers of the corona around the leader. An attachment instability enhances the electric field leading to strongly inhomogeneous, bright and locally warmer regions ahead of the leader that explain the existing observations. Since the attachment instability is only triggered by fields above 10 kV/cm and internal electric fields are lower in positive than in negative streamers, our results explain why, although common in negative leaders, space stems and stepping are hardly observed if not absent in positive leaders. Further work is required to fully explain the streamer to leader transition, which requires an electric current persisting for timescales longer than the typical attachment time of electrons, around 100 ns.

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Cited by in corpus (7)

• The physics of streamer discharge phenomena
• Observations of the Origin of Downward Terrestrial Gamma-Ray Flashes
• Radio emission from negative lightning leader steps reveals inner meter-scale structure
• On the emergence mechanism of carrot sprites
• A computational study of accelerating, steady and fading negative streamers in ambient air
• Streamer propagation in humid air
• The emission of energetic electrons from the complex streamer corona adjacent to leader stepping