The above photograph of a Superior Mirage near the Isle of Skye in Northwest Scotland, with the Isle of Harris beyond, was taken by Alison Dunlop, on 22nd April 2020, when the air pressure was quite high, at 1028mb:
Mirages are caused by light refracting abnormally as it travels along layers of air of different temperatures. Superior mirages occur mainly in the Arctic regions in the Spring, when warmer air overlays colder air, known as a thermal inversion.
Abnormal refraction at sea can cause navigational errors and accidents. The most famous example of this is the Titanic disaster, which occurred in the North Atlantic on April 15 1912, when the pressure was also very high, at about 135mb:
Mirage strips frequently appear as fog banks on the horizon, because of the depth of air you can see through in the duct, even when the weather is otherwise completely clear. The Vikings called these apparent fog banks ‘Hafgerdingar’ meaning ‘sea hedges’.
Titanic sank in the freezing waters of the Labrador Current in the North Atlantic, surrounded by dozens of large icebergs, some of which were 200 feet high. But above the level of the top of those icebergs much warmer air drifted across from the nearby warmer waters of the Gulf Stream, trapping cold air underneath it.
These temperature differences can be seen from the thermal image of sea surface temperatures, above, where the freezing Labrador Current flows into the much warmer waters of the Gulf Stream.
This created a thermal inversion at Titanic’s crash site , creating apparent fog banks or “sea hedges” around the horizon, despite the perfectly clear weather.
In fact several ships which passed through the area in which Titanic sank, both before and after the tragedy, recorded abnormal refraction and mirages at the horizon.
The night the Titanic sank was also calm and clear, but Titanic’s lookouts noticed the mirage strip appearing like a band of haze stretching all around the horizon, as they entered the thermal inversion in the ice region.
Titanic did not slow down because the weather was so clear that her officers expected to see ice in time to avoid it. But the optical effect of the apparent fog bank around the horizon reduced the contrast with the iceberg, causing Titanic’s lookouts to see it too late.
As Titanic’s lookout, Reginald Lee, explained at the Inquiry into the sinking of the Titanic, the fatal iceberg suddenly appeared as a dark mass out of the peculiar haze in front of them:
‘What sort of a night was it?– A clear, starry night overhead, but at the time of the accident there was a haze right ahead – in fact it was extending more or less round the horizon. There was no moon.
And no wind?– And no wind whatever, barring what the ship made herself.
Quite a calm sea?– Quite a calm sea.
Was it cold?– Very, freezing.
Did you notice this haze which you said extended on the horizon when you first came on the look-out, or did it come later?– It was not so distinct then – not to be noticed. You did not really notice it then – not on going on watch, but we had all our work cut out to pierce through it just after we started. My mate happened to pass the remark to me. He said, “Well; if we can see through that we will be lucky.” That was when we began to notice there was a haze on the water. There was nothing in sight.
You had been told, of course, to keep a careful look-out for ice, and you were trying to pierce the haze as much as you could?– Yes, to see as much as we could.
What did the [iceberg] look like?– It was a dark mass that came through that haze and there was no white appearing until it was just close alongside the ship, and that was just a fringe at the top.
It was a dark mass that appeared, you say?– Through this haze, and as she moved away from it, there was just a white fringe along the top.
Quite right; that is where she hit, but can you tell us how far the iceberg was from you, this mass that you saw?– It might have been half a mile or more; it might have been less; I could not give you the distance in that peculiar light.
The Wreck Commissioner:
I mean the evidence before and after the accident is that the sky was perfectly clear, and therefore if the evidence of the haze is to be accepted, it must have been some extraordinary natural phenomenon…’
Unfortunately, Titanic’s lookouts were not believed, but these recent photographs of ‘flying ships’ show the unusual atmospheric phenomenon which caught out Titanic’s experienced officers.
Even more tragically, the abnormally raised horizon behind the Titanic caused her to appear to the nearby Californian to be a 400ft ship only five miles away, when in fact she was the 800ft Titanic, sinking about 10 miles away.
That optical illusion caused the Californian’s Captain to believe that what they thought was a relatively small nearby ship had no radio, as they knew the only ship in the area with radio that night was the Titanic.
So Californian instead signalled Titanic by Morse lamp, but the stratified air in the thermal inversion, combined with the much greater than apparent distance to Titanic, caused the Morse lamp signals between the two vessels to appear like randomly flickering masthead lamps.
In the final nail in Titanic’s coffin that night, her distress rockets were exploding in the normally refracting air high up, but Titanic’s hull was seen distorted through the very cold air nearer the sea surface, which optical effects combined to make Titanic’s rockets appear very low.
These unusual optical phenomena caused comprehension errors on Californian which meant that the nearest vessel to Titanic took no action to rescue her 2,200 passengers from the freezing waters of the North Atlantic.
The sinking of the Titanic remains the world’s worst peacetime maritime disaster, costing the lives of 1,500 men, women and children.