When I fly in some of the less populated parts of the world; Africa, Northern Canada, or Eastern Europe, I see these solid from afar and transparent from up close columbs rising from the ground. However, if I am someplace more populous, such as the US or West-Middle Europe, they are no where to be found. Has anyone seen them before or know what could be a cause? Thanks in advance.

But then again you are flying a F-106 in unauthorized airspace!