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The behavior of lightning discharges is intimately linked with the kinematics and resulting precipitation structure of the parent thunderstorm. Ice particles become charged through collisions in the thunderstorm updraft, which also sorts them by mass in the cloud. In normal-polarity storms, small ice crystals preferentially acquire a positive charge by losing electrons to larger graupel pellets rimed with supercooled liquid water. The charge separation that leads to lightning occurs as small ice particles collect near the cloud top while the massive graupel accumulates in the mid-levels of the storm. Charged ice particles can also be advected from the convective core of the thunderstorm into the leading anvil or trailing stratiform region. The laterally-expansive charge layers that result from advection (and local in-situ charging in the stratiform region) produce lightning with long horizontal channels that can extend over hundreds of kilometers.
Ground-based Lightning Mapping Array (LMA) measurements were first used to document lightning extremes, and identified one flash that was 321 km in length and another that lasted 7.74 s. Both of these cases were stratiform flashes with long horizontal channels. Due to the limited line-of-sight domains of LMA networks, extreme lightning must occur near the center of the array to be completely resolved, and still there are limits to the scale of lightning that can be measured by an LMA. Since these extreme flashes are exceptionally rare, this ideal configuration is unlikely. Space-based lightning imagers can resolve the lateral development of stratiform flashes without the range limitation. Moreover, the Geostationary Lightning Mapper (GLM) on NOAA's GOES satellites provides staring coverage of the entire western hemisphere. Extreme lightning over the Americas can be mapped by GLM wherever and whenever it occurs. In 2018, I documented cases of GLM flashes that were up to 673 km in length, that lasted up to 13.496 s, and that covered a cloud-top area of 114,997 km^2.
Optical lightning observations are also modified by the thunderstorm precipitation structure through scattering and absorption. In extreme cases, a lightning flash may not be detected if its optical emissions must traverse a thick layer of cloud to reach the satellite, or a detected flash may have its appearance changed to reflect the cloud scene. Flashes that occur near the side of the storm can illuminate the top of a nearby lower cloud layer, causing the satellite to detect lightning events over a 10,000 km^2 area. It is important to take into consideration how the optical signals from lightning are modified by scattering across the cloud scene when analyzing the characteristics of flashes or pulses reported by lightning imagers like GLM. However, these effects also generate opportunities for characterizing the thundercloud illuminated by lightning. I developed an algorithm that uses the relative frequency of these large yet stationary lightning flashes compared to horizontally propagating lightning flashes to assess whether thunderstorms observed by GLM are in the developing stage (more lightning near the edges of the storm) or mature stage (more propagating flashes). I also developed a technique for producing cloud imagery from lightning imager data that describes the vertically-integrated layer between the source and the satellite.
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.
Peterson, M. J., W. Deierling, C. Liu, D. Mach, C. Kalb, 2016: The properties of optical lightning flashes and the clouds they illuminate. J. Geophys. Res., 122, 116, 423-442.
Peterson, M. J. and C. Liu, 2013: Characteristics of Lightning Flashes with Exceptional Illuminated Areas, Durations, and Optical Powers and Surrounding Storm Properties in the Tropics and Inner Subtropics, J. Geophys. Res. Atmos., 118, 11,727-11,740, doi: 10.1002/jgrd.50715