Spectral Output of Sprites From Both Conventional and Runaway Breakdown

There has been much scientific interest in understanding the physical processes that lead to high-altitude optical transients (i.e. sprites). Are sprites formed through conventional breakdown, runaway breakdown, or both? The optical results of an improved model (UNIMAX) including runaway and conventional breakdown are presented. Optical, radio, and g-ray emissions have previously been calculated using a version of this model that did not include conventional ionization or magnetic pinching. The electromagnetic algorithms in UNIMAX now include the important effects of induction and radiation. A momentum equation for the relativistic electrons, which allows the effect of magnetic pinching to be modeled, has been added to the equation set. The current paper describes the optical emissions from the new model and elucidates the differences found by including the new features of the model. Optical emissions for both primary and secondary electrons are calculated using fluorescence efficiencies from Davidson and O?Neil, quenching rates from Mitchell, and atmospheric transmission data from Guttman. The temporal characteristics of several lines, including 337.1 nm, 391.4 nm, 399.8 nm, 427.0 nm, and 427.8 nm are presented and compared with previous photometer measurements and previous results of other models. Line ratios of N2 2P (i.e. 399.8 nm) and 1N (i.e. 427.8 nm) transitions are presented and analyzed to identify more precisely what diagnostic information about the discharge plasma can be deduced from such observations. Model outputs are compared with data and the differences between conventional breakdown models and those based on the simultaneous occurrence of both processes are delineated.