Fog has occurred almost daily at Summit since we’ve been here, typically in the “evening” as the sun gets lower in the sky (it never actually sets right now, just dips down to a few degrees above the horizon).  As the sun goes down, the surface cools, as does the atmospheric boundary layer, leading to condensation.  The fog is often very thin, as seen to the left (that is a 47 m tower in the background).  There have been times when layers are only about 1-2 meters thick and you can clearly see below and above.   And often there are fog bows opposite the sun.  The layering is rather phenomenal, and the boundary layer depth often decreases to only 10-20 m thick.