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X-ray bursts associated with leader steps in cloud-to-ground lightning

Dwyer, J. R.; Rassoul, H. K.; Al-Dayeh, M.; Caraway, L.; Chrest, A.; Wright, B.; Kozak, E.; Jerauld, J.; Uman, M. A.; Rakov, V. A.; Jordan, D. M.; Rambo, K. J.

Geophysical Research Letters (2004), Volume Date 2005, 32(1), L01803/1-L01803/4 CODEN: GPRLAJ; ISSN: 0094-8276. English.

X-ray and elec. field measurements were made during 5 nearby neg. natural lightning strikes in north central Florida during the summer of 2004. The observed x-ray emission typically was detected ~1 ms before the 1st return stroke, during the stepped-leader phase, and had energies extending up to a few hundred keV. The X rays were produced in discrete, intense bursts emitted in coincidence with the formation of the leader steps, demonstrating unambiguously that the source of lightning X rays is closely related to the stepping process. The x-ray emission from lightning stepped leaders is found to be remarkably similar to that from lightning dart leaders, suggesting that these different types of leaders share a common mechanism. The reported observations have important implications for understanding how runaway breakdown occurs and how lightning leaders propagate.

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