Arctic Mirages¬†–¬†August 7, 2019

Today’s Science Wednesday is about Arctic mirages. I took this photo from the bridge of the Polar Pioneer, a 70-meter long ship with reinforced hull for ice breaking.

The image shows a “fata morgana” of the coastline in the Arctic Ocean. This optical phenomenon occurs because rays of light are bent when they pass through air layers of different temperatures in a steep thermal inversion. A thermal inversion is an atmospheric condition where warmer air exists in a well-defined layer above a layer of significantly cooler air. This temperature inversion is the opposite of what is normally the case; air is usually warmer close to the surface, and cooler higher up.

In calm weather, a layer of significantly warmer air may rest over colder dense air, forming an “atmospheric duct” that acts like a refracting lens, producing a series of both inverted and erect images. A fata morgana requires a duct to be present, as a thermal inversion alone is not enough to produce this kind of mirage. While a thermal inversion often takes place without there being an atmospheric duct, an atmospheric duct cannot exist without there first being a thermal inversion.