Energetics

Color camera observations of sprites and blue jets from 1994 provided the first information about the energy processes producing middle atmospheric optical emissions (Sentman et al.(1995b),Wescott et al.(1995)). The optical signature from sprites appeared primarily in the red channel of the color camera with some blue emissions from the lower portions of sprites. Blue jets appear solely in the blue channel. Spectrographic observations of sprites in 1995 identified the brightest red emissions as the molecular nitrogen first positive group (N₂(1PG)) (Hampton et al.(1996),Mende et al.(1995)). Ground based blue filtered photometer observations and blue and red filtered observations were made in the summers of 1996, 1997, and 1998 to understand the blue emissions of sprites (Armstrong et al.(1998),Suszcynsky et al.(1998)). Most observations of optical emissions above thunderstorms are made at low slant angles (10^o or less), so severe Rayleigh scattering is present and atmospheric transmission in the blue is poor (c.f. Section 2 of (Morrill et al.(1998))). The EXL98 (Energetics of Upper Atmospheric Excitation by Lightning, 1998) campaign was designed specifically to study microphysical energy processes of sprites, blue jets, and elves. EXL98 (Sentman et al.(1998)) was centered on a series of aircraft flights during July 1998 with several intensified cameras. These cameras covered wavelengths from the near-UV (320 nm) to the near-IR (>1500 nm) and provided a unique opportunity to study the energetics of these phenomena. One reason for the use of aircraft in 1998 was to get above the dense atmosphere to facilitate blue observations.