ATOMOSPHERIC GAMMA RAYS. As if thunderstorms don't do enough by sending buckets or rain and thunderbolts to the ground, they are now known to produce gamma radiation with energies up to 10 MeV. Physicists at the University of Bologna in Italy have observed two kinds of gammas in their scintillation detectors: lower-energy gammas (less than 3 MeV) from radioactive aerosol particles descending in rainfall and higher-energy gammas (up to 10 MeV). Previously researchers had seen photons with energies only up to hundreds of keV, and only then by using detectors mounted in planes or on balloons.

The Bologna results (Menotti Galli, menotti.galli@bo.infn.it) were recorded on a mountain at Gran Sasso, where interesting physics experiments are also going on underground (WIMP detectors; see Update 472). The more potent gammas are most likely emitted by electrons in the atmosphere coming to rest after having been accelerated to high velocities by electric fields associated with lightning. A similar mechanism is thought to be responsible for other weird atmospheric emissions such as "red sprites" and "blue jets." (Brunetti et al., Geophysical Research Letters, 1 June /pnu/2000/.)