I have just finished the lectures on how light and infra-red radiation affect the weather as part of one of our introductory meteorology courses. It is pleasing when nature throws you a nice example at the right time.
It is always hard to get over the point that the long-wave thermal infra-red radiation is important as the short-wave solar radiation, simply because people do not have built in sensors that work in the thermal infra-red. So it is good to find examples where you can see the effects of the longwave radiation. Here, the downwelling radiation from the trees is greater than that from the sky, so the ground under the trees has not cooled enough overnight for frost to form.
This one features not only a mock sun or parhelion, but also some nice crepuscular rays, which are an example of scattering. The photo isn’t that good because it was taken through the window of a moving train — it is both pleasing and frustrating how many optical phenomena I see during my commute.