Near-Infrared Atomic Oxygen Photometry of Lightning

Abstract

Measuring the temperature of lightning is a fundamental part of understanding the evolution of the plasma channel, and it is also crucial to quantify its chemical and energetic impacts in the atmosphere. Nonetheless, due to complications that have both to do with the complexity of the source and required equipment, this has only been done in a few studies to date. Here we report on the design and implementation of an instrument to perform simultaneous, multi-band optical and radio observations of lightning, which aims to provide a fast and simple way to routinely measure its temperature. The primary instrument includes photometers to measure temperature and electric field sensors to identify lightning sub-processes. Data are analyzed in tandem with 2D and 3D lightning location information. To measure the temperature, the photometer array includes 3 channels equipped with narrowband filters (1 nm) centered at bright atomic oxygen lines in the near-infrared, and temperature is given from the relative intensity of optical emissions across the 3 channels. We found the average peak temperature of 44 negative cloud-to-ground lightning return strokes to be 17,600 K. Additionally, the peak temperature had no apparent correlation to the peak current. Comparisons between 777 nm observations from the ground and from space by the Geostationary Lightning Mapper (GLM) emphasize the picture that the instruments in these two vantage points tend to see different portions of the lightning flash. They also reveal that dart leaders play a key role in the interpretation of lightning observations from space.