Numerical simulation of a lightning seed formation in a thundercloud

It is presently unclear how lightning channel forms inside a thundercloud, where maximal electric field strengths are about an order of magnitude lower than the dielectric strength of air. Recently, a hypothesis has been formulated, according to which a lightning leader forms inside a hierarchical network of plasma channels that fills an area of increased intracloud electric field. The study proposes a numerical model that is used to simulate the transition from separate streamer systems to complex plasma structures which segments are characterized by a wide spread of electrical parameters. Those clusters, which are sufficiently extended along an intracloud electric field vector, can be considered as lightning seeds. It is shown that their formation is a fairly collective process that can occur in electric fields lower than positive streamers propagation threshold. Depending on considered conditions, the required spatiotemporal frequencies of streamer systems appearance are shown to be less than or of the order of those of hydrometeors collisions (or nearly collisions) in a thundercloud. The altitudes of 6 and 9 km, which are the most typical for lightning genesis, are considered to analyze how the factor of air density influences the features of a lightning seed formation process.