Lightning in Wildfire Smoke Plumes Observed in Colorado during Summer 2012

Pyrocumulus clouds above three Colorado wildfires (Hewlett Gulch, High Park, and Waldo Canyon; all during the summer of 2012) electrified and produced localized intracloud discharges whenever the smoke plumes grew above 10 km MSL (approximately −45°C). Vertical development occurred during periods of rapid wildfire growth, as indicated by the shortwave infrared channel on a geostationary satellite, as well as by incident reports. The lightning discharges were detected by a three-dimensional lightning mapping network. Based on Doppler and polarimetric radar observations, they likely were caused by ice-based electrification processes that did not involve significant amounts of high-density graupel. Plumes that did not feature significant amounts of radar-inferred ice at high altitudes did not produce lightning, which means lightning observations may assist in diagnosing pyrocumulus features that could affect the radiative characteristics and chemical composition of the upper troposphere. The lightning was not detected by the National Lightning Detection Network, implying that pyrocumulus lightning may occur more frequently than past studies (which lacked access to detailed intracloud information) might suggest. Given the known spatial and temporal advantages provided by lightning networks over radar and satellite data, the results also indicate a possible new application for lightning data in monitoring wildfire state.

Joint radio and optical observations of the most radio-powerful intracloud lightning discharges

The most radio-powerful intracloud lightning emissions are associated with a phenomenon variously called "narrow bipolar events" or "compact intracloud discharges". This article examines in detail the coincidence and timing relationship between, on the one hand, the most radio-powerful intracloud lightning events and, on the other hand, optical outputs (or lack thereof) of the same discharge process. This is done, first, using coordinated very high frequency (VHF) and optical observations from the FORTE satellite and, second, using coordinated sferic and all-sky optical observations from the Los Alamos Sferic Array. In both cases, it is found that the sought coincidences are exceedingly rare. Moreover, in the handful of coincidences between optical and intense radio emissions that have been identified, the radio emissions differ from their usual behavior, by being accompanied by approximately simultaneous "conventional" lightning radio emissions. It is implied that the most radio-powerful intracloud emission process essentially differs from ordinary incandescent lightning.