Modeling of Sprite Optical Emissions From Runaway and Conventional Breakdown and Comparison to Measurements
Abstract
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 a combination of both depending on conditions? In this paper, we describe the calculation of optical emissions associated with two different simulations performed with a 2-d fully electromagnetic discharge model (UNIMAX). Optical emissions driven by primary electrons (runaway breakdown) are calculated using measured fluorescence efficiencies and quenching rates for each wavelength of interest. For the secondary electrons (conventional breakdown and secondary electrons sustained in an electric field that lies below the conventional breakdown threshold), the emissivity of nitrogen bands as a function of electric field are used to estimate the optical emissions for the N2 1P, 2P, and N2+ 1N bands. We developed a methodology to split the band results into individual transitions. In addition, we include absorption from the source to an observer at a specified height. We present simulated camera images, line ratios, and spectra for a typical sprite and a carrot-type sprite. We compare our model results in detail to measurements to identify more precisely what diagnostic information about the discharge plasma can be deduced from such observations. The differences between conventional breakdown models and those based on the simultaneous occurrence of both processes are delineated.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFMAE21A1100T
- Keywords:
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- 3304 Atmospheric electricity;
- 3324 Lightning