Superior Mirage of Kaiserstuhl Mountain Range

May 03, 2011

Photographer: Stephan Danner
Summary Author: Stephan Danner; Jim Foster

The photo above shows a superior mirage of the Kaiserstuhl Mountain Range in southern Germany on the morning of February 7, 2011. The Kaiserstuhl is an ancient volcanic mountain rising to 1,826 ft (557 m). It's approximately 15.5 mi (25 km) distant from the location where I snapped the picture. Note the exaggerated flat topped summits, which attain the same altitude as that of the dingy atmospheric layer in the background. On this mid-winter morning, there was an intense inversion -- warm air trapped above cooler air at the surface. Inversions typically occur when the surface undergoes radiational cooling; the stored surface heat is radiated (by longwave emission) into a calm, clear sky. When such cooling is ongoing for several hours, which is often the case on the longer nights of autumn and winter, the temperature immediately above the surface in low lying locations is noticeably cooler than air several feet to, in some instances, hundreds of feet higher. Such inversion layers act to trap contaminants (hence the smoggy appearance) and distort light. Rays of sunlight are bent or refracted toward the ground by the inversion layer, so from my perspective, the mountaintops loom above the valley in the midground. With a superior mirage, an object looks higher than its true position.