Early Model of Lightning Spectrum Generation with PIC-DSMC

Cloud-to-ground lightning strikes are generally a sequence of multiple steps of streamer-leader progression, including branching, followed by a strongly conducting arc once the strike has grounded. Different plasma chemistry is active in each of these different phases, and the spectrum generated by each of these phases is also different. This work begins an effort to produce a time history of spectra for a lightning strike from initial streamer-leader steps to final conducting channel, including continuing currents. To do so, a model of air breakdown mimicking lightning is first performed in an implicit PIC-MCC simulation code, Chicago. A time history of reduced plasma state (e.g., gas density, electron temperature, etc.) is extracted from the large-scale simulation and handed off to an explicit PIC-DSMC simulation code, Aleph, which is capable of directly tracking photons and large speciation sets. Aleph is then exercised in a 0D mode to achieve quasistatic plasma states and their associated spectra. Aleph will track molecular and atomic species of nitrogen and oxygen, including electronically and vibrationally excited states. Photonic chemistry is also included (e.g., photoionization). Differences in spectra from different stages of the lightning strike will be presented.