Dodging and Burning

Here's a strange one.  I was out on St. Catherine's Hill again this afternoon, or rather, walking along the remnant ridge facing the hill, which is the western side of the deep cutting through Twyford Down that accommodates the M3 motorway.  The light was pretty, and there was a warm southern wind blowing: a nice day for a walk, and I was carrying a Fuji X100 to keep things light.

I always like this view, because of the interest that wiggly track down into the valley gives to an otherwise bland green vista:

However, in the process of adjusting the image this evening, I noticed something both odd and annoying.  Above the main clump of trees on the crown  of the hill there appeared to be a bright halo, very like the sort of artefact that would result, back in the darkroom days, from a bit of clumsy "dodging" i.e. selectively blocking some of the light from the enlarger with a card disc mounted on a wire, in order to brighten up a dark area.  Looking at it more closely, however, I could see that it appeared to be "real", in the sense that it wasn't just a bit of lens flare, or some other such optical artefact.  There really was a bright halo around the trees.

So, I crunched down the brightness, to bring it out, and this is what resulted:

Ignore the cyan coloration, which is an artefact, but look at the shape and texture of the halo.  Note that we are looking west, and the wind is coming from the south i.e. the left side of the picture, and it's around 15:30, so the sun is moderately low in the sky, off to the south-west.  I would say it's clearly some kind of brightly-illuminated turbulent flow, emanating from the trees, or from somewhere immediately behind, and blowing away to the north.  But what?

It's possible it's smoke from burning cleared undergrowth, which happens all over the hill, though that seems unlikely on a Sunday.  Also, immediately on the other side of the clump is the Mizmaze, which is a protected monument, and not a place where any responsible person would build a bonfire.  Of course, mentioning the Mizmaze opens the door to all sorts of bonkers speculation, but we won't go there.  Most likely, I think, is that it is simply the trees giving off water vapour after some heavy rainfall yesterday.  Curious, though, and not something I've ever noticed before.