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Lightning is nature's way of neutralizing the charge imbalances in thunderstorms that arise from charge transfer during ice particle collisions. A lightning "flash" consists of a series of breakdowns starting in the cloud that may work their way towards the ground and strike the surface. These breakdowns occur as the air becomes ionized under an intense electric field. They are often measured as a series of "steps" with finite lengths in high-speed photography that extend the existing lightning channel. Electrical breakdowns in virgin air produce strong radio emissions. Arrays of synchronized VHF-band radio receivers can locate the breakdown source and map the development of lightning channels. RF signatures of cloud pulses differ from positive and negative Cloud-to-Ground strokes. Thus, VHF waveform data from broadband receivers can reveal what type of discharge produced the recorded radio signals.
While VHF radio measurements detect electrical breakdowns, optical and acoustic instruments sense current flow down the lightning channel. The air becomes heated to temperatures exceeding 20,000 K (hotter than the surface of the sun), and the major atmospheric constituent gasses become dissociated. This causes strong optical emission (particularly at atomic lines for nitrogen and oxygen) that can be measured from great distances, and a shockwave from thermal expansion that we hear as thunder.
Optical lightning measurements show where strong currents are flowing in the lightning "tree" structure, and can be used to identify physical lightning processes during favorable viewing conditions including stepped leaders, CG strokes, and continuing current. High background radiances and intervening clouds add uncertainty to the optical signals. This is the primary challenge for space-based investigations of lightning physics, as there will almost always be a cloud layer between the source and sensor when viewed from above that will modify the optical signals from the discharge through scattering.
A combined-phenomenology approach is ideal for studying lightning physics because it can benefit from the strengths of RF and optical lightning measurements while mitigating the weaknesses each observation type would have in isolation. I am interested in mapping the evolution of lightning in traditionally data-sparse regions, identifying signatures of physical lightning processes measured from space, and examining how optical signals emitted by lightning interact with the surrounding cloud medium. I use a combination of ground-based and space-based optical and RF sensors to investigate these topics.
Publications
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Boggs, L. D., N. Liu, M. Peterson, S. Lazarus, M. Splitt, F. Lucena, A. Nag, H. K. Rassoul, 2019: First observations of gigantic jets from geostationary orbit. Geophys. Res. Lett., 46, 7, 3999-4006.
Peterson, M. J. and S. Rudlosky, 2018: The time evolution of optical lightning flashes. J. Geophys. Res., 124, 1, 333-349.
Peterson, M. J., S. Rudlosky, and W. Deierling, 2018: Mapping the lateral development of lightning flashes from orbit. J. Geophys. Res., 123, 17, 9674-9687.
Peterson, M. J., S. Rudlosky, and W. Deierling, 2017: The evolution and structure of extreme optical lightning flashes. J. Geophys. Res., 122, 24, 13,370-13,386.