A TGF launches gamma rays (magenta) and high-energy electrons (yellow) and positrons (green) into space.  Gamma rays emerge from the atmosphere in a broad beam. Electrons and positrons, moving at nearly the speed of light, travel into space along the Earth’s magnetic field. Calculations show that the high-field regions near a TGF may produce biologically significant radiation doses. Image Credit: NASA/GSFC & J. Dwyer/Florida Inst. of Technology.
A TGF launches gamma rays (magenta) and high-energy electrons (yellow) and positrons (green) into space. Gamma rays emerge from the atmosphere in a broad beam. Electrons and positrons, moving at nearly the speed of light, travel into space along the Earth’s magnetic field. Calculations show that the high-field regions near a TGF may produce biologically significant radiation doses. Image Credit: NASA/GSFC & J. Dwyer/Florida Inst. of Technology.

Objectives

  • Advance the understanding of particle acceleration and radiation transport in thunderstorms, which have only recently been understood to generate both intense flashes and continuous glows of ionizing radiation. Thunderstorms are the most powerful natural accelerators on Earth.
  • Address questions of the intensity distribution, the altitude range of the origin of the emission, the variations of TGF spectra at the source, the beaming characteristics of the radiation, and the type(s) of lightning that are associated with the production of ionizing radiation.

Approach
Observing TGFs from space with Fermi:

  • NRL leads new science topic for Fermi Large Area Telescope. NRL and collaborators will periodically turn Fermi 'on its head', pointing it at the nadir as it passes over active terrestrial thunderstorm regions; Fermi LAT will probe the emission spectra—and thus underlying physical processes—and localization/correlation of the energetic emission with lightning events
  • The combination of large field of view and large collecting area makes Fermi ~30 times more sensitive than previous missions

Future plans:

  • Leverage existing X-ray and gamma ray detector systems developed in NRL SSD to observe TGFs at minimal cost
  • Ground and airborne measurements of X-rays, gamma rays, and neutrons from thunderstorms, coordinated with radio-frequency imaging of lightning events

Deliverable/Value/Accomplishment

  • NRL-delivered Fermi results demonstrate robust temporal correlation with lightning flashes and best estimates of total radiation fluence in low Earth orbit
  • NRL-led coordinated radio imaging and gamma ray spectroscopy will be used to derive TGF generation mechanism, location, occurrence rate and radiation fluence/dose at atmosphere and from orbit