TIME-RESOLVED SPRITE IMAGERY

Fleeting columns of luminosity occurring above large thunderstorms at 50-90 km altitude, presently known as sprites, were imaged with an int ensified video charge coupled device (CCD) camera during a July 1995 g round-based campaign near Fort Collins, Colorado. These unfiltered int ensified images reveal detailed spatial structure within the sprite en velope. The temporal resolution of standard interlaced video imagery i s limited by the 60 fields per second acquisition rate (16 ms). The sp ecific CCD used here, however, is subject to bright events leaking int o the readout registers, allowing time-resolution on the order of the linescan rare (63 mu s). Typical sprite onset is found to follow the a ssociated cloud lightning by 1.5 to 4 ms. The onsets of the individual sprites within a cluster are generally, but not always, simultaneous to within 1 ms. Sprites tend to have a bright localized core, less tha n 2 km in horizontal dimension, which rises to peak intensity within 0 .3 ms and maintains this level for 5 to 10 ms before fading over an ad ditional 10 ms.