An optical illusion caused the ship in the Gulf of Paria to appear as though it was hovering above the horizon. (Karen Johnstone, October 18th 2018)
You may have seen images of a ‘hovering’ ship circulating on social media, spotted off the coast of England.
This phenomenon, called a superior mirage, is not unique to temperate regions of the world. While it is most common in the Arctic and Antarctic, it can appear anywhere special atmospheric conditions occur that bend light.
What causes a superior mirage?
Meteorologically, this phenomenon occurs as a result of a temperature inversion near the surface of the ocean (or any other large water body).
In a usual atmospheric setup, temperature decreases as altitude (or height) increase. In rare circumstances, even in T&T, the temperature just above the sea or ocean is cooler than the warmer air above it.
The mirage appears when a layer of warm air sits above your line of sight with a cool layer beneath it. Light bends down towards the denser air, but because our eyes assume the light we see travels straight, the object we are seeing appears higher than it actually is. Therefore we see the image, or inversions of it, above where it actually is. This bending of light is a process called refraction.
Generally, if another ship sails away from you, eventually, they will disappear below the horizon. However, if conditions create superior mirages, you can still the other ship further away from you even though the ship is a short distance below the horizon. Similarly, with the refraction of a superior mirage, you can see mountain tops sooner as you sail toward a mountainous island or coastline, even though the mountain top might still be slightly below the geometric horizon.
In the Gulf of Paria, this phenomenon was captured by Karen Johnstone off Trinidad’s northwestern coast, during the morning of 18th October 2018.
Superior mirages can produce different types of ‘hovering’ ships, where distant objects appear to float above their actual position, as was the case in the Gulf of Paria. It can also make objects below the horizon become visible, which is more common for mariners.
What is that on the horizon?
The atmosphere is a turbulent place. Sometimes, when the temperature inversion is not even, you may see a Fata Morgana. This could be caused by several layers of warm and cold air that cause a combination of superior and inferior mirages. Because of the uneven inversion, light is refracted in strange ways, creating multiple segmented reflections of the original image, with some sections towering high above the water. The image created by a Fata Morgana is usually much less recognizable than that in a mirage and often appears as floating walls or castles.
The name of this mirage comes from Fairy Morgan (or Fata Morgana in Italian) of the King Arthur legend, an enchantress/magician who could create illusions of floating castles.