I suspect the curved formation could be some sort of accessory cloud under the cumulus perhaps drawn into a curve by a local area of vorticity or convergence zone but I'm blindly guessing.
Bit of a tricky one. Brian, any ideas?.
Not really, the only phenomena I've seen like that are shock waves ... you didn't hear a bang, did you? (Maybe up to a minute later)
The association with the position of the Sun appears to be "accidental" but it's possible that the effect would have been invisible if it occurred somewhere else in the sky i.e. it needed the Sun to be close by to make the "wall" visible.
It looks as though the effect is either disrupting the higher thin broken layer or is a seperate thin layer underneath it as the structure of the altocumulus (?) layer is fuzzed out in the vicinity. The presence of the iridescence suggests that the water droplets in the cloud are very uniform in size, which would suggest that the cloud is just forming. That, I think, is a clue to one possible cause - suppose a rising warm dry air bubble bursts through a thin layer of air which is saturated vapour without droplets, forcing it to rise & cooling it enough to start condensing, whilst the bubble of warm air passes through (and eventually makes its own cumulus head). But this is theoretical, as I say I've never seen it like this - the dimensions look about right for a typical weak thermal, though. What usually happens is that the warm air bubble is more humid than the surrounding air (because it's come from a warmer level, and has picked up more moisture) so it saturates & starts to condense rather than the air it drags up with it.
Really I don't know.
