Winter Road Surface Inferior Mirage

March 02, 2011

: Gregory Read 
Summary Author: Gregory Read; Jim Foster

When the weather is hot, highway mirages are familiar to most people. However, when it's -10 F (-23 C), road surface mirages are not as easily observed. Nonetheless, if the roadway is heated a few degrees above the ambient temperature, a mirage may appear at the road-air interface, just as it does when it's 90 F (32 C). As shown above, on Highway 11 between Regina and Saskatoon, Saskatchewan, the blue sky seems to have swallowed a portion of the road in the mid-ground. A shallow layer of relatively warm air lies just above the road surface. The difference in the refractive index between the warmer air and the much denser, frigid air above it creates a boundary, which behaves as would a mirror. So, distant objects, in this case the sky, are reflected. Because the reflected image appears below the real object (sky), this is an inferior mirage. The driver of the car from which this photo was snapped doesn't need to be concerned about plowing into this wall of blue since it's, well, just a mirage. Photo taken on February 20, 2011.

Photo details: Camera Maker: NIKON CORPORATION; Camera Model: NIKON D100; Focal Length: 210.0mm (35mm equivalent: 315mm); Aperture: f/14.0; Exposure Time: 0.0016 s (1/640); Exposure Bias: +1.00 EV; Metering Mode: Center Weight; Exposure: aperture priority (semi-auto); White Balance: Manual; Light Source: Unknown; Flash Fired: No; Orientation: Normal; Color Space: sRGB.