My brother took a number of pictures in the alps recently, and a few of these showed defects similar but not identical to the one below. The temperature was -14 C which doesn't seem unreasonably cold. Any ideas what this might be? Full res here.
Edit: Here are the color versions, and it's still somewhat unclear if it's Newton's rings or some other effect.
I could be very well wrong, but those look a lot like Newton's rings, which can be caused by two layers of dissimilar materials that are normally in close contact expanding or contracting differently, making one of them buckle slightly. And by slightly, I mean that the spacing between them varies by fractions of a wavelength of light. (Another, similar possibility is differential stress polarization effects, again with a thermal basis. It's really hard to tell in B&W, though.) The "origin" of the pattern probably indicates a relative "hot spot". If the camera is shot cold, or allowed a little while to warm up completely, you probably wouldn't see a problem, but if it's been on just long enough to partially warm up, there might be enough difference in temperature across the sandwich that is the sensor, its lenses and filters, to cause a visible pattern.
This looks like the sun was just outside the picture. While it is therefore not imaged directly, the secondary reflections from the various lens elements do end up in the picture.
This is exactly why you see people shading their lens when they point it near the sun. Try to arrange the picture so that the sun is not just outside the image. That makes it easier to use your hand or something to shade the lens but without it ending up in the picture.
