Physics and Astronomy Space Plasma Seminar - Professor Joseph R. Dwyer, UNH
Title: "Dark Lightning"
Abstract: Dark lightning is a large-scale electrical discharge inside thunderstorms that was only recently identified. Unlike normal lightning, which involves a hot conductive channel, dark lightning occurs when large numbers of energetic runaway electrons are accelerated by thunderstorm electric fields. These energetic electrons ionize the air, causing very large currents to flow, rapidly discharging parts of the thunderstorm. Observations suggest that the currents may reach several hundred thousand amps, making these discharges some of the largest in our atmosphere. Models show that, as a by-product, dark lightning generates enormous fluxes of MeV gamma rays, which can explain terrestrial gamma-ray flashes (TGFs) seen from spacecraft in low-Earth orbit. Furthermore, because the discharge does not involve a hot, incandescent channel, the amount of visible light produced is much less than that from normal lightning and would not be visible to the human eye in most cases. In this presentation, I will discuss dark lightning modeling and observations and other related phenomena in the field of high-energy atmospheric physics.