re: Yes, but since they gave these comments.
"The energies we see are as high as those of gamma rays emitted from black holes and neutron stars," said David Smith, an assistant professor of physics at UC Santa Cruz and author of a scientific paper on this topic.
The exact mechanism that accelerates the electron beams to produce TGFs is still uncertain, he said, but it probably involves the build-up of electric charge at the tops of thunderclouds due to lightning discharges. This results in a powerful electric field between the cloudtops and the ionosphere, the outer layer of Earth's atmosphere.
http://www.nasa.gov/vision/universe/solarsystem/rhessi_tgf.html
I wondered if there was more than electricity involved. Like something to do with nuclear energy.