Revision 1

Accepted · first revision · record

Title: How does lightning start in fields far below breakdown?
Plain: Air normally conducts only in very strong electric fields, about ten times stronger than any measured inside a storm. Something lets lightning start anyway.
Precise: Maximum measured in-cloud fields are of order 5 to 10 statV/cm, roughly an order of magnitude below the conventional breakdown field at cloud altitudes. Identify the initiation sequence: field enhancement at hydrometeors launching streamers, seeding by cosmic-ray relativistic runaway electrons, or fast positive breakdown. An answer is a quantitative model reproducing radio-mapped initiation events (timing, extent, current) from measured fields and hydrometeor properties.
Settled by: Simultaneous in-cloud field and hydrometeor measurements with high-resolution radio interferometry (e.g. LOFAR) at the initiation point.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)