When someone mentions the word "mirage," most of us conjure up the image of a thirsty desert traveler, crawling on hands and knees toward a shimmering pool of water that isn't really there. On a more personal level, you may have driven in hot weather and seen "water" on the roadway ahead that never gets any closer.

Both phenomena are caused by hot air close to the surface and cooler air above. The dramatic temperature difference causes light passing through the layers to bend (refract) toward the warmer air. In the case of the hot roadway, the "water" is actually an image of the sky near the horizon that now appears on the road surface. Since the image of the sky appears below where it normally would, this type of mirage is called inferior.

Mirages don't restrict themselves to areas that are hot. They can occur anywhere there are large vertical temperature differences. Here in Antarctica, we have mirages of our own. They typically occur when winds are nearly calm over a broad area and very cold air pools at the surface. Mirages in this situation are called superior mirages because, with warmer air above the cold surface layer, we see objects above their actual position. This appearance of elevated images is commonly called looming.

These figures show a few of the different ways looming can manifest itself. The first figure represents a normal view of an island surrounded by sea ice. The second and third figures show what you'd see if you were above the coldest layer of air (most frequent in McMurdo). The lowest portion of the island may be stretched vertically or you may see the entire image of the island elevated above the ice. The last figure depicts what you'd see if you were within the coldest layer of air. Not only is an image elevated above the island, it's inverted.

While looming doesn't occur with great regularity, your best bet to observe it will be under widespread calm conditions while watching the area where sea ice and land meet on the far side of McMurdo Sound.