Mirages

Mirages (Photos by Glenn Shaw)

Though most people associated mirages with a hot desert environment----mirages of a palm tree grove torturing the dry traveller---there are actually more numerous and more spectacular mirages at the polar latitudes. These photos show some examples of a polar mirage seen from the University of Alaska campus at Fairbanks. What we see is a greatly distorted image of a low hill about 10 miles away. Normally this is merely a small bump, but on the day of this mirage, the atmosphere was acting like a lens and a mirror. The "lens" is making the hill rise up higher than normal and taking on a new shape, the "mirror" is causing an upside down reflection.
The distorted views are brought about by strong thermoclines (temperature variations) within the atmosphere. In some cases the air temperature can vary by ten degrees over a few tens of meter altitude change. Sometimes the temperature changes with height constitute "inversions", where the normal situation of it becoming colder as you ascend is "inverted" and it becomes warmer. Also, there are occasionally strong temperature alterations, either decreasing or increasing strongly with heights and confined to narrow layers. The cause of these layers is poorly understood, but sometimes is associated with waves that can propagate through the atmosphere. These layers can "trap" or duct images, and cause upside down reflections like those we see in this photograph. Such strong temperature structures tend to be typical during the cold, dark months in the Arctic and Antarctic. Because of this, things are not necessarily as they seem or appear to be, and there are many tales of early polar explorers being misled, thinking they were heading by dogsled to mountains....which ultimately never appeared because they were nothing more than a "mirage".