What would make a circle cloud like this?

I think this was even closer to a perfect circle before I asked my wife to take this photo, it broke up shortly after. Does anyone know of an atmospheric phenomenon which causes perfectly circular clouds? Microcomets, atomic testing, alien craft, dumb luck? The sun was a few dozen degrees to the left, but this wasn't like any Sun dog, I've ever seen. It isn't a lens flare either, since three of us saw it before we bothered with the camera.

(No I'm not going to tell you that they took us into their spaceship and toured their planet out yonder, just past Vega.)

A localised circular aircurrent could do that. If there was something on the ground to trigger a spiral action and then a small cloud floated in.

Mind you you normally see that kind of thing near moutain riges where the air gets turbulent and eddies are more likely.

I'd put this one down to 'dumb luck' as you put it.

Bart.

The inside is dark therefore it is not an empty circle it is a filled disk-like cloud formation.
Probably a coincidence.
Look at the clouds long enough and you are likely to see anything !

A localised circular aircurrent could do that. If there was something on the ground to trigger a spiral action and then a small cloud floated in.

Mind you you normally see that kind of thing near moutain riges where the air gets turbulent and eddies are more likely.

I'd put this one down to 'dumb luck' as you put it.

Bart.

It's pretty flat here near upper broadmeadows estuary, Malahide/Swords area. But the warm shallow brackish water, a motorway overpass, small hills and nearby cold sea can have an odd influence on the weather. Last summer I saw and took a really bad photograph of a 1000+ foot high dust devil (or whatever you call micro-tornados) twirling over the far side of the estuary. I thought that was strange because I'm certainly not in Kansas anymore. I guess (almost) anything is possible!

The inside is dark therefore it is not an empty circle it is a filled disk-like cloud formation.
Probably a coincidence.

Yes, that's probably it. Sometimes its difficult to tell rare phenomenon like sun dogs, glorys and sun cats (made that up) from the random stuff that just happens.

Look at the clouds long enough and you are likely to see anything !

I'll have my camera ready when I see O = 2πr spelled out in clouds or better yet a circle wih the first few digits of pi in base e .

I saw the complete works of Shakespeare written in the clouds a few years ago.
I just didn't have my camera handy at the time.