at sunset some shadows just come in and out of existence, seems to be the angle of the sun against background objects like hills and bridges before they fuller render in properly. Motegi GP is a prime example, there were a couple more but cant remember off the top of my head i dont use lens flare or god rays btw
Another example is Daytona oval in afternoon (or sunset, or bevlieve), this happens everytime in one of the turns (I think the final one).