Electric fields and electron energies in sprites and temporal evolutions of lightning charge moment

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Abstract
The fundamental electrodynamical coupling processes between lightning and sprites are investigated. By combining the observed spectral data with the Monte Carlo swarm experiments, reduced electric fields and electron energies in sprite streamers and halos are estimated. The obtained fields inside sprite halos (70-97 Td with an analysis error of +/- 5 Td) are lower than the conventional breakdown field, E-k similar to 128 Td, indicating a significant reduction of electrons associated with halos while those in sprite streamers (98-380 Td with an error of +/- 50 Td) are higher than Ek, suggesting that a significant ionization process drives their formation and development. A combined analysis of photometric and electromagnetic data makes it possible to estimate temporal evolutions of lightning charge moment. It is found that lightning discharges with a short time scale (similar to 1 ms) and a moderate amount of charge moment (similar to 400 C km) produce discernible halos. On the other hand, lightning discharges with a large amount of charge moment (similar to 1300 C km) produce streamers regardless of their time scale. The results obtained are comprehensively interpreted with both the conventional breakdown field necessary for the formation of streamers and the electric field necessary for the production of optical emissions of halo which is sensitive to the time scale of the thundercloud field due to the significant reduction of electrons.