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Article

enter image description here

BBC meteorologist David Braine said the "superior mirage" occurred because of "special atmospheric conditions that bend light".

He said the illusion is common in the Arctic, but can appear "very rarely" in the UK during winter.

Mr Braine said: "Superior mirages occur because of the weather condition known as a temperature inversion, where cold air lies close to the sea with warmer air above it.

What is happening here?

Why is the surface of the water, where it touches the boat, not "bent" equally with the boat itself?

Why is this common in the arctic?

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    $\begingroup$ From The Guardian with a nice diagram and more detail on the HyperPhysics page. $\endgroup$
    – Farcher
    Mar 6 at 8:57
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    $\begingroup$ @Farcher: Those sources seem not to address the main question, which is: "Why doesn't the surface of the water appear equally elevated?" $\endgroup$
    – WillO
    Mar 6 at 13:23
  • $\begingroup$ @Willo The water is elevated but the it blends into the sky as a diagram in the HyperPhysics site shows. $\endgroup$
    – Farcher
    Mar 6 at 16:10
  • $\begingroup$ I just signal that the same visual can happen without a Fata Morgana, just due to an almost perfect match of the far part of the sea and the sky. I witness that relatively often. $\endgroup$
    – Alchimista
    Mar 10 at 12:15
  • $\begingroup$ @WillO does it mean that chromatic merging of sea and sky (as I mentioned above) happens in fata Morgana? I see now the bases that prompted OP to ask.. $\endgroup$
    – Alchimista
    Mar 10 at 12:18
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This effect is also called Fata Morgana, or mirage.

Fata Morgana, mirage that appeared periodically in the Strait of Messina between Italy and Sicily, named in Italian after the legendary enchantress of Arthurian romance, Morgan le Fay [Source]

What is happening here?

The optical phenomenon occurs because rays of light are bent when they pass through air layers of different temperatures in a steep thermal inversion where an atmospheric duct has formed. (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; 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. [Source]

Here are two visual aids:

  • In this one one may see that there are various mirages possible of happening

enter image description here

(Source)

  • This one focuses on Superior mirages, the one that appears to be present in the case you mention

enter image description here

(Source)

Why is the surface of the water, where it touches the boat, not "bent" equally with the boat itself?

As @Farcher pointed out

The water is elevated but the it blends into the sky.

Here you'll be able to find additional diagrams that may help.

Why is this common in the arctic?

A Fata Morgana is most commonly seen in polar regions, especially over large sheets of ice that have a uniform low temperature. It may, however, be observed in almost any area. In polar regions the Fata Morgana phenomenon is observed on relatively cold days. In deserts, over oceans, and over lakes, however, a Fata Morgana may be observed on hot days.

To generate the Fata Morgana phenomenon, the thermal inversion has to be strong enough that the curvature of the light rays within the inversion layer is stronger than the curvature of the Earth. Under these conditions, the rays bend and create arcs. An observer needs to be within or below an atmospheric duct in order to be able to see a Fata Morgana. [Source]

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tl;dr: The popular explanation of this image is likely wrong. It could be, rather, an inferior mirage.

Many news articles claim this is a superior mirage, that is, one that's due to a temperature inversion. Here's an image borrowed from hyperphysics that shows the idea: warm air lies above cold, and the rays bend toward the slower medium (the colder air) causing objects near the horizon to appear higher. Superior mirage.

I am QUITE CONFIDENT that this in not the correct explanation for the image in question. The photo was apparently taken over the southern English Channel in February 2021. The water temperature, and therefore the temperature of the air very close to the sea surface, was around 10 C. The air a bit higher up was likely colder (weather records show that it was never far above 10 C in that month, and often considerably below). Rather than a superior mirage, it could be an inferior mirage (assuming it's not a fake)--the same kind as causes the appearance of water on a hot road. The rays near the surface bend upward, causing them to cross those that originate at a slightly higher angle. The actual mirage is not the ship, but the sky below it. Here is a sketch:

Inferior mirage

The result is that the ship does not appear distorted--the rays from it don't deflect--and the distortion that would be apparent in the rays that do deflect doesn't appear because there are no features in the sky to distort.

This actually happens routinely on chilly days where I live--albeit to less dramatic effect. A thin strip of sky appears below distant land. It is definitely an inferior mirage as it happens exclusively on days when the air is colder than the water (usually below freezing). I took this photo with my phone after seeing the reporting on the Cornwall mirage:

Island mirage

If I'd had a telephoto lens rather than a cell phone, the depth of the apparent layer of sky would appear similar to that in the Cornwall image (though the level of detail likely would not measure up).

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  • $\begingroup$ Your hand-drawn image doesn't explain why there's no water to the left and right of the ship. I think the ray between the camera and the ship should be already curved, but if it doesn't intersect the ship (as on the sides), it continues curving upwards, into the sky. $\endgroup$
    – Ruslan
    Mar 10 at 12:55
  • $\begingroup$ @Ruslan I have edited the drawing in response to your comments. Hopefully now it's clear why you don't see water behind the ship. $\endgroup$
    – Ben51
    Mar 10 at 16:36
  • $\begingroup$ Still doesn't look convincing. As you lower the angle of view, the "SHIP" line will scan the ship from top to bottom, until the ray gets into the warm air. This is OK. But then, lowering angle of view further should result in the ray gradually going higher (aiming to become the lower "SKY" ray), scanning the ship bottom to top, which would result in inverted image right under the upright one. In other words, the transition from "SHIP" to lower "SKY" line should be continuous, while here it appears to be abrupt, exactly at the place where the inverted image is to be hidden. $\endgroup$
    – Ruslan
    Mar 10 at 17:42
  • $\begingroup$ @Ruslan I agree with you. All I can suggest is that the inverted image may be so compressed vertically as to be invisible. I am not certain that it’s an inferior mirage and not a fake or an illusion where the water beyond a certain distance somehow looks like sky. But I am pretty certain it’s not a superior mirage. $\endgroup$
    – Ben51
    Mar 10 at 20:05

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