The research project will quantitatively investigate the effects of both natural and rocket-triggered lightning in the mesosphere-lower thermosphere-ionosphere (MLTI) region of the atmosphere between 60 and 100 km altitude. The experimental effort will focus on several outstanding questions regarding the production of light-emitting phenomena known collectively as transient luminous events (TLEs) by natural lightning and will investigate the possible role of rocket-triggered lightning as a source for these disturbances. The primary theoretical effort will combine state-of-the-art numerical models to predict the mesospheric/ionospheric reaction to realistic return-stroke currents consistent with observations. The experimental effort centers on lightning observed at and near the International Center for Lightning Research and Testing (ICLRT) in Camp Blanding, Florida. The project will provide simultaneous wideband (1 Hz-20 MHz) observations of the causative lightning waveforms (both natural and rocket-triggered), photometric observations for the optical detection of transient luminous events, and narrowband (200-Hz bandwidth) observations of very low frequency (VLF, 3-30 kHz) signals that are sensitive to conductivity changes in the D-region ionosphere. These systems will provide continuous monitoring of ionospheric events related to natural lightning throughout the three-year period of the award. Attempts to trigger lightning using the classical rocket-and-wire technique will be performed during intense nighttime thunderstorms. This program will address the following questions: 1) What are the wideband (1 Hz-20 MHz) characteristics of lightning that successfully produce TLEs? 2) What are the wideband characteristics of lightning that successfully produce ionospheric conductivity changes that scatter VLF signals? 3) What characteristics of TLEs are most closely associated with the observed VLF scattering?
