High speed image sequence of a cloud-to-ground lightning stroke, from cloud exit to ground attachment. The duration spanned by these images is 6 milliseconds. My group recorded these images in Colorado during an experimental campaign.
Lightning
It is surprising that as common as lightning is, many aspects of how it starts and propagates are not very well understood. My group uses a variety of tools, such as instruments to measure the radio emissions from lightning, high speed cameras to capture optical details, and electromagnetic modeling and simulation, in an effort to answer some of those open questions.
We do a lot of work with radio instrumentation. We were among the pioneers of using the electromagnetic fields radiated by lightning as a tool for measuring the details a variety of lightning processes, and we have developed an operational real time network for remotely measuring the transfer of electric charge in lightning. Currently our instruments are deployed in more than 10 locations across the US, Central and South America, and Africa.
Amazingly, thunderstorms sometimes are able to create and launch upwards into space short bursts of very high energy gamma rays, electrons, and even antimatter. These terrestrial gamma ray flashes or TGFs came as a huge surprise when the phenomenon was first reported in 1994, and we still don't understand quite how it happens. Relying mostly on our radio instrumentation, we were among the first to show that TGFs are produced inside thunderclouds, not at high altitudes. We also showed that there is a distinct radio signature that is simultaneous with the gamma-ray generation in the cloud. This is probably produced by the gamma ray production process itself and could provide important clues into the internal physics.
Some of Our Recent Lightning-Related Papers
Analysis of radio measurements showing that the structure of the lightning flash in the cloud influences the strength of a lightning stroke to the ground: Lu, G., S. A. Cummer, R. J. Blakeslee, and E. McCaul, Lightning morphology and impulse charge moment changes of high peak current negative strokes (2012), J. Geophys. Res., v. 117, D04212. [pdf reprint]
Simultaneous radio and satellite measurements of TGFs identifying a distinct radio emission during TGF generation: Cummer, S. A., G. Lu, M. S. Briggs, V. Connaughton, S. Xiong, G. J. Fishman, and J. R. Dwyer (2011), The lightning-TGF relationship on microsecond timescales, Geophys. Res. Lett., v. 38, L14810. [pdf reprint]
Multi-frequency radio measurements showing that TGFs are produced during the early stage of ordinary in-cloud lightning flashes: Lu, G., R. J. Blakeslee, J. Li, D. M. Smith, X.-M. Shao, E. W. McCaul, D. E. Buechler, H. J. Christian, J, M. Hall, and S. A. Cummer (2010), Lightning mapping observation of a terrestrial gamma-ray flash, Geophys. Res. Lett., 37, L11806. [pdf reprint]