That would fall in line with my previous post about cloud seeding. They mentioned something about the particles creating ice crystals in the cold part of the cloud, which then fall into the warm part of the cloud, causing rain.
This appears to be a phenonomon called a SUNDOG. It is essentially a clear sky circular rainbow, usually forming in atmospheric ice. It is called a Sundog, because it circles the sun. Last time I saw one in person was when I was at Yellowstone a few years back.