Found this AP photo on Yahoo! News:
Caption:
Unusual ring-shaped smoke is formed when U.S. Air Forces A-10 Thunderbolt II attack aircraft was shooting imitation bombshells toward the ground during Air Power Day at the U.S. airbase in Osan, south of Seoul, South Korea, Sunday, Oct. 12, 2008. The Air Power Day is not only a demonstration of U.S. Air Power, but also the U.S. partnership with the South Korea Air Force. The event was part of an annual ceremony to open the U.S. airbase to South Korean people.
(AP Photo/ Lee Jin-man)
Anybody from our \"Hog\" professionals who can/will explain that?