RAPID LATERAL EXPANSION OF OPTICAL LUMINOSITY IN LIGHTNING-INDUCED IONOSPHERIC FLASHES REFERRED TO AS ELVES

Data acquired by a new array of horizontally spaced photometers boresi ghted with a low-light-level camera provide the first measurement of t he rapid lateral expansion of optical luminosity in lightning-induced ionospheric flashes referred to as 'elves', occurring over time scales substantially less than 1 ms. The narrow individual fields-of-view of (2.2 degrees x 1.1 degrees) provide a spatial resolution of similar t o 20-km at a range of 500 km, enabling the documentation of expansion occurring over a horizontal range of 200 km with a time resolution of similar to 30 mu s. The observed dynamic features of elves are consist ent with a model in which the optical output is produced as a result o f heating by the electromagnetic pulse (EMP) from a lightning discharg e.