I read this a few days ago on Reddit. The first thing I thought about was the Catatumbo lightning storm. There is constant lightning every single day or so in Venezuela. Then I reread the wiki page and there is a mention of a high uranium concentration in the area so it might be a source of gamma rays, but I really doubt it is sufficient to generate that much lightning, or such a phenomenon would be much more common.<p><a href="http://en.wikipedia.org/wiki/Catatumbo_lightning" rel="nofollow">http://en.wikipedia.org/wiki/Catatumbo_lightning</a>
The atmosphere as a kind of spark chamber? <a href="http://www.hep.phy.cam.ac.uk/~lester/teaching/SparkChamber/SparkChamber.html" rel="nofollow">http://www.hep.phy.cam.ac.uk/~lester/teaching/SparkChamber/S...</a>