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Airborne Image Measurements of ELVES Over Southern Europe

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ELVES appear as rapidly expanding horizontal disks of light at the base of the night-time ionosphere due to the absorption of electromagnetic pulse (EMP) energy generated by powerful cloud-to-ground (CG) lightning discharges (with peak currents typically >80 kA). They were first postulated in 1993 to explain unusual transient limb "brightenings" observed at mesospheric airglow heights (~90 km) from the Space Shuttle, and subsequently were measured using ground-based high speed mapping array photometers (Fukunishi et al., 1996). Elves occur within a few hundred µs of the parent lightning discharge, well ahead of the onset of sprite emissions. Modeling and recent satellite measurements have shown that they can attain a diameter of a few to several hundred kilometers and usually exhibit a characteristic "donut shape" with a dark central hole (for a near vertical CG). To date, most ELVE studies have been performed using specialized narrow-field photometer arrays (e.g. Barrington-Leigh et al., 2001) that are capable of measuring their temporal evolution during their very short lifetimes (<0.5 ms), but not their integrated two-dimensional structure.


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