"Waghorn" wrote

Remarkable photo.Searching for 'doughnut' or annular cloud on Google finds
nothing comparable (but lots of whacky stuff).
IN his book 'Satellite as Microscope' RS Scorer shows satellite images of
an annular cloud off the coast of Portugal but 50-100Km across.
I would guess it's a thermal interacting with the layer of stratus,but
it's location over orography is also highly suggestive of a flow induced
vortex .
Any more pictures,approx dimensions ,was it rotating as a whole?The
vortices over the low countries were at least an order of magnitude
larger and almost certainly have a different dynamical origin,

I'll contact Andy with your query.

Don't forget he was at 23,000 feet at the time, so that doughnut cloud was
almost certainly too high to be thermal generated. I'm not sure if he got
up to that height by means of normal lee waves. Andy?

Jack