Initiation of lightning discharges without electrodes and at low breakdown fields

Determine the physical mechanism that initiates lightning discharges within thunderclouds given the absence of electrodes and the observation of low breakdown fields, clarifying how discharge onset occurs under these atmospheric conditions.

Background

The paper emphasizes that natural lightning differs markedly from laboratory discharges, particularly because it occurs in the atmosphere without defined electrodes and often at electric field strengths lower than standard breakdown values. This discrepancy complicates direct application of laboratory breakdown theory to thunderstorms.

The authors note prior investigations into contributions from metastable oxygen and nitrogen to reduce breakdown thresholds and time-domain simulations of preliminary breakdown pulses. However, they stress that, despite these efforts, a definitive explanation for how lightning initiates under these conditions has not been achieved, motivating their proposed alternative mechanism based on transient metallic bonding and resonant-percolation pathways.