"Road Blink" Southern Alberta, Canada February 22, 2009 imaged by Alan Clark of the University of Calgary. ©Alan Clark, shown with permission.

"A couple of photos of what I call 'road blink', taken in light fog in Southern Alberta during our drive back from Arizona last weekend."

The fog/sky above the dark road is darker than elsewhere. " I think that this effect is equivalent to the blink seen in arctic regions and used to find breaks in ice."   Patterns of light (snow) and dark (water leads) are echoed onto a cloudy sky and can be used as a map. See also a 'Potomac blink'

"Reflection upwards from the road into the fog is fainter than reflection from snow in neighbouring fields, leading to an apparent dark tunnel into which one appears to drive."

The images possibly also show mirage effects. "Snow had fallen a day or two ago but it was probably light and would have blown off [the road] easily. The design of roads in this part of the world, with shallow ditches on either side, allows this to happen. The sun [in late February] is high enough to produce some heating on the dark road surface. The pictures were taken in the early afternoon (1:52pm, about 1 hour after highest sun angle for this longitude)."

"The lines of snow across the road at various points were probably produced by vehicles or snowmobiles crossing the road, since they seem to occur at or near intersections or opposite farm buildings. The latter vehicles leave a distinctive narrow trail."

"There were mirages all along this road, so some at least of this light across the road [and headlamp 'reflections' - too cold for water pools] COULD be mirage effects." - Inferior 'hot road' mirages produced by a road warmed air layer below much colder air.

"This is a relatively common sight in winter in these parts. It is often sufficiently intense to produce the illusion of driving in a tunnel, somewhat disconcerting, psychologically!"


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