Why does snow behave in two mutually exclusive ways?
Pictures 1-4 - top row:
Here the snow mimics the pattern of the underlying surface.
Pictures 5-8 - bottom row:
Here the snow inverts the pattern of the underlying surface.
I have only vague ideas what might cause this:
- the hollows in the underground conduct heat differently than the tiles and protect the snow from melting,
- the hollows in the underground cause eddies in the air-stream and this accumulates more snow.
Marcel Minnaert does not mention this phenomenon (I think), but I will have to search his books again.