Summary

The scientific objective of SPRITE SPECTRA-II is to determine the physical processes involved in sprites, and in particular the ionization of molecules in the blue part of the light spectrum. The blue light cannot be adequately observed from ground-based measurements, or by viewing through the normal GV windows as was done in the 2009 SPRITE SPECTRA flights. The sprites typically start 70-80 km above thunderstorms and move downwards over a 50 km altitude range.

 The project scientists will continue earlier analysis work and use high-speed imagers to record sprites with high temporal and spatial resolution. They propose to use slit-less spectroscopy to obtain sprite spectra with ~500 m altitude, 0.1 ms (or possibly less) temporal and 10 nm spectral (400-800 nm) resolution. For high spatial resolution they plan to use a telescope with 3 m spatial and possibly <100 ms temporal resolution.

 SPRITE SPECTRA-II will use the NSF/NCAR GV to fly as high as possible at about 200 km distance from thunderstorms and will likely target Mesoscale Convective Systems, MCS, due to their high number of lightning strikes.

 SPRITE SPECTRA-II is based on an already NSF-funded project through ATM Aeronomy. The instrument package consists of two cameras mounted with the same viewing axis. One (the imager) will be mounted inside a normal GV window, the other (the spectral instrument) will view through a new side-looking optical window, thus extending the transmissivity down to about 275 nm by using fused silica window panes. The fused silica window panes have almost 100% transmissivity well below the atmospheric limit of 360-370 nm for severe absorbtion. The side-looking optical window will be a RAF development project which requires a Supplemental Type Certificate (STC)  The PIs need to be able to change the elevation angle and the heading angle of the instruments by about 30 degrees to point effectively at the sprite region above thunderstorms. EOL will manufacture automated pivoting mounts for both cameras and mount them on two half-height rack.