Polar illusion: trying to see through nature’s tricks - Edu Arctic

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Polar regions hold many mysteries, including some of the last places on Earth yet to be reached by man. Hidden deep under the ice and cut off from the outside world for thousands (or even millions) of years, Antarctic lakes are likely to be inhabited by bacteria, which may fundamentally change our understanding of the origins of life on the planet and, for all we know, its existence elsewhere in space. Scientists do their best to see the invisible, without being led astray by appearances, which tend to be particularly deceptive in ice-covered lands. Extraordinary polar conditions favour illusion, which tricked the Vikings and even today – initially at least – might make us think of aliens. As usual, however, bewildering though they are, the phenomena can all be explained by science.

Burning ocean

Some phenomena, despite their bizarre appearance, have simple and intuitive explanations. Let’s take for instance the so-called sea smoke. Even though at first glance it may seem that the sea surface is on fire, a closer look reveals that it’s just a mist made up of frozen water vapour. Because the sea is at least 10°C warmer than the air, seawater evaporates and immediately condenses, creating the curious smoking-sea effect. The phenomenon is especially common in the Arctic, but – every once in a while – it may also be observed over the surface of the Baltic Sea.

Inuit navigation

In the past, a particular role was played by optical phenomena observed in the sea-and-ice landscape of the Arctic Ocean. Their telltale English names include, among others, iceblink and water sky. The former is a white-yellowish glow visible on the underside of low clouds, over a distant cluster of compact ice. When sunlight penetrates the clouds, it is reflected between the layer of clouds and the surface of the Earth. Water absorbs solar radiation a lot better than ice, so clouds passing over open water remain dark. Those passing over ice-covered areas, however, become lit underneath with the light reflected off the surface of ice. Even a relatively small area of ice creates a clearly visible glow, which can be seen from a considerable distance.

Water sky, on the other hand, refers to dark patches on the underside of low clouds, which indicate the presence of open water amidst sea ice (under the clouds). As has already been mentioned, sunlight reflects off the surface of water differently than it does off ice. And while light bouncing off an ice-covered surface lights up the bottom layer of low-lying clouds, a break in the ice cover means that much of the light becomes absorbed by water and the clouds over the area remain dark.

These phenomena served as natural lighthouses, warning the Inuit people and polar daredevils looking for the Northwest Passage about dangerous sea ice which might have been out of view or even beyond the horizon.

By the way, although the ability to read natural phenomena surely helped polar explorers to avoid danger, it did not help them one bit to find what they were looking for. In 1795, after two hundred years of searching, it was finally concluded that a continuously navigable Norwest Passage simply doesn’t exist. The northern route from the Atlantic to the Pacific could theoretically be completed, but it would take years, as ships would have to spend many months trapped in ice. Due to global warming the situation is now changing, with a potentially significant shipping lane gradually opening up in the North. The new passage, however, will create not only opportunities, but also a whole range of environmental hazards.

The hafgerdingar saga

Water sky and iceblink are exceptional among optical phenomena. They’re “innocent” or even advantageous, as – by exaggerating reality – they make it possible to recognise danger or choose the right route from a larger distance and without specialist equipment. Unlike these natural navigational aids, other optical illusions were anything but helpful, misleading cartographers, who marked on their maps non-existent islands.

Early Norse sagas, such as “Konungs skuggsjá” (“The King’s Mirror”) from the 13th century, mention the so-called hafgerdingar. “The King’s Mirror” is a dialogue between a father and a son, in which the son, seeking wisdom and understanding, asks his father about the world. In the part entitled “Marvels of Greenland”, the father describes mysterious “sea hedges”, which look “as if all the waves and tempests of the ocean have been collected into three heaps, out of which three billows are formed (…) they are higher than lofty mountains and resemble steep, overhanging cliffs”. These sea hedges filled brave Norse warriors with terror, sometimes making them flee their ships in panic, as they had no way of knowing that what they saw were simply Arctic mirages (also referred to by the Icelandic name “hillingar”) or images of land located far beyond the horizon.

Hafgerdingars form because the air lying close to cold ground is denser than the warmer air further above and, as such, has a light-bending effect. In other words, they are displaced images of distant objects, not unlike Fata Morgana, which can be observed in the world’s deserts (and which was named after sorceress Morgana from the Legend of King Arthur). Regardless of where they occur, mirages are caused by the refraction of light in air layers of varying temperature.

Arctic mirages are examples of the so-called superior mirages, which differ from their desert equivalents in that the light rays bend the opposite way. In case of a desert mirage, the image is upside down and lower than the original object. Hafgerdingars, on the other hand, make the objects appear the right side up but higher than they really are.

How does a superior mirage form? The layer of air lying close to the ground is cooler and therefore denser than the layers above it. This makes light rays bend towards the bottom layer, causing a mirror reflection to occur. What the observer sees is an image of an object which in fact lies below his line of sight, beyond the horizon. As a result of atmospheric refraction, or the bending of light-rays in the atmosphere, the objects are seemingly “lifted”, which makes them visible from a much greater distance.

Even though Arctic mirages were often met with fear and confusion, some found them fascinating and covered vast distances chasing fantastic lands “suspended” above the surface of the ocean. It is probably due to mirages that people sailing in Arctic waters knew what to expect beyond the horizon. It is also likely that the shores of Iceland were reached for the first time in small, simple boats because the crews were drawn forward by a mirage of the Faroe Islands, located 385 km further. They didn’t get that far, but – by a lucky twist of fate – they came across Iceland.

Novaya Zemlya – sun in the night sky

One of the most mysterious, spectacular and rare examples of an Arctic mirage is the so-called Novaya Zemlya effect. The phenomenon was first observed by the members of the ill-fated Dutch expedition searching for the Northwest Passage and recorded in the diary of Geritt de Veer. The expedition failed, but it became famous anyway as the crew – with the famous Willem Barents as its helmsman and navigator – discovered Spitsbergen and Bear Island. Not long afterwards, near Novaya Zemlya, the ship was trapped in ice and crushed, but the crew managed to survive. The only exception was Barents, who died of scurvy in June 1597.

De Veer wrote in his diary about the terrifying darkness and no hope for daylight. On 24 January 1597, however, amidst the darkness, a “miracle” happened. Two weeks before the expected, tentative return of the Sun after the polar night, the exhausted crew noticed bright light in the sky. Initially, they thought they were hallucinating or that they had made a mistake in their calculations, but the light appeared again. After the crew made it back home, however, their accounts were called to question. Three centuries later another famous polar explorer witnessed the same phenomenon, this time near the southern edges of the world. It was Sir Ernest Shackleton, during his last expedition to Antarctica in the years 1914–1917. He saw the sun rising seven days after it had set for the season, and then again two months later, five days before its expected return. Still, it was only in 1956, five years after the effect was once again spotted in Antarctica, that it was finally acknowledged as an authentic natural phenomenon.

The Novaya Zemlya effect is an illusion of the Sun rising during a polar night, which is a result of an optical channel forming in the lower level of the atmosphere. As most mirages, it is caused by significant differences in air temperature over the surface of ice. A strong temperature inversion, with a colder layer of air found underneath a warmer layer, creates favourable conditions for the effect to occur. The inversion layer, however, must be at least 400 km thick, which is extremely rare and which is why the phenomenon has only been witnessed a handful of times. The sunlight is caught under the thermocline, which means it can be observed even though the Sun itself remains below the horizon.

The Bible and close encounters of the third kind

Spectacular physical phenomena, believed to have been caused by supernatural powers, feature in many mysterious and dramatic passages in the Bible. The following account comes from Ezekiel – one of the most famous prophets of the Old Testament – who described what he had seen with his own eyes: “Like the appearance of a rainbow in a cloud on a rainy day, so was the appearance of the brightness all around it. This was the appearance of the likeness of the glory of the Lord. So when I saw it, I fell on my face, and I heard a voice of One speaking.”

According to scientists, these words may have been inspired by yet another type of an optical illusion, known as parhelion or a sun dog, which looks like an additional sun in the sky. The phenomenon takes the form of bright patches of light appearing on both sides of the Sun, usually about 22° to the left and to the right of it, at the same altitude above the horizon.

What we actually see is the Sun’s reflections formed in ice crystals found in clouds. Sun dogs appear most readily when air temperature is very low, but they are not limited to polar regions. They may occur wherever cirrus clouds (composed of ice crystals) appear in the sky.

For those supporting the theory that the ancient world was visited by extraterrestrial beings, the above passage and other vivid accounts of Ezekiel are evidence of UFO encounters. Even today, many optical phenomena observed in the sky are interpreted this way. It is especially true of the so-called sun pillars. This amazing phenomenon is rare outside the Arctic and it used to be reported as irrefutable evidence of the UFO. Sun pillars look like vertical beams of bright light stretching from the sky towards the ground or the other way round. It is, of course, no more than an optical illusion, which occurs when natural or artificial light (from the Sun, the Moon, or even a street lamp) gets reflected by ice crystals. Sometimes, on very cold days, flat ice crystals (known as diamond dust), which can normally be found only in high clouds, float in the air close to the Earth’s surface and their vertical sides reflect the light downwards, creating a unique spectacle.

It’s great to be able to see through the optical illusions encountered in polar regions and outside of them. Knowing the mechanism behind them, however, should not diminish our appreciation of their remarkable and somewhat otherworldly beauty.


Author: Anna Wielgopolan