Novel Remote Measurements and Analysis of Continuing Lightning Current

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This grant enables the installation and operation of equipment at Duke University for measuring the ULF (ultra low frequency) magnetic field associated with certain lightning discharges. A strong and long-lasting current sometimes flows after lightning strokes in the conducting channel they leave behind. Called the continuing current, it is not well understood but is a detail of the physics of lightning that is thought to be related to cloud electrification and to phenomena in the high atmosphere such as sprites and elves. Continuing currents produce signals in the ULF magnetic field that can be detected as far as 2000 km from the lightning source. Methods will be developed on this project to detect continuing currents remotely and infer their duration and waveform from ULF measurements. The data interpretation will be validated by comparing measured waveforms of the continuing currents associated with triggered lightning at a field station in Camp Blanding, Florida, with the waveforms inferred from ULF measurements. A goal is to continuously record the magnetic fields from lightning discharges detectable at the Duke ULF station and relate the measurements to storm structure and meteorological conditions. If the continuing current turns out to be related to storm severity or stage of evolution, it may be a useful tool for the study and forecasting of storms.