A Very Deceiving Night: Sea Hedges

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Sea Hedges

Sometimes mirages are easy to spot as they appear like a wall around the sea:

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Superior mirage of islands, photograph by Pekka Parviainen

But sometimes they appear just like a bank of fog or mist on the horizon.

As Dr. Andrew T. Young, one of the world’s leading atmospheric refraction experts explains:

“The superior mirage is often associated with an appearance of “fog” at the horizon, because one sees much farther than usual in the mirage strip below the “false horizon””.  

Because air is not completely clear, the more of it you are looking through – i.e. the further you are seeing – the more scattered light you get between you and the object viewed and this is what appears as a haze.  This is evident whenever one can see a long way, for example, when viewing a mountain range at thirty miles.

In fact, as Dr Young goes on to explain:

“Even perfectly clean air still scatters some light. The molecules themselves, though much smaller than the wavelengths of light, can still scatter a little. But, because the molecules are smaller than the wavelength, they scatter short wavelengths (which are more nearly comparable to the size of the molecules) better than long wavelengths.

This scattering by particles much smaller than the wavelength was first studied by Lord Rayleigh in 1871. Because he worked out the details of this process, it’s generally called “Rayleigh scattering.”

Rayleigh scattering is the cause of the blue sky: the shortest wavelengths of sunlight (blue and violet) are scattered better than the longer ones, and the average color of the scattered light is the blue of the sky. This color is much more intense than the pale blue of aerosol scattering.

Because the short wavelengths are selectively scattered, the remaining direct sunlight contains mostly the longest wavelengths: red and orange. That’s why the setting Sun looks reddish. This removal of light by scattering is the main component of atmospheric extinction.”

Because you can see a long way in a mirage and therefore there is a greater depth of air to scatter light, for centuries sailors have confused miraging on the horizon with a bank of fog or haze and the following photographs show very clearly how superior mirages can appear like fog, mist or a haze on the horizon:

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A mirage appears off the shore of Penglai City in eastern China’s Shandong Province on Sunday, May 7, 2005. Photo: China Photo Press

 As reported in the Chinese press at the time: “Mists rising on the shore created an image of a city, with modern high-rise buildings, broad city streets and bustling cars as well as crowds of people all clearly visible. Thousands of tourists and local residents witnessed a mirage of high clarity lasting for four hours off the shore of Penglai City in east China’s Shandong Province on Sunday”:

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A close-up of a part of the mirage “mist” off the shore of Penglai City in east China’s Shandong Province.  In fact, though the jumbled mirage image looks like city blocks it is in fact merely the miraging of an ordinary shoreline.  It is only our brains which convert this confusing image into an ordered cityscape.

Photo: China Photo Press

In his essay, “On the temperature, fogs and mirages of the river St. Lawrence,” published in Transactions of the Literary and Historical Society of Quebec 3, 1–45 (1832), W. Kelly states:

“There was generally with the mirage an appearance of a fog bank on the horizon . . . . The air within the horizon was at the same time perfectly clear.”

An early account and drawing of a superior mirage published in Gentleman’s Magazine 63, 601–602 (1793) by the Chaplain of the Dunkirk Man of War, the Rev. Samuel Dickenson L.L.B, is called “A Description of a Phenomenon caused by Haze seen at Sea Aug. 10, 1759” and in the account he points out:

“The term haze, prefixed to the foregoing account, is adopted from the phrase then used by the sailors, perhaps improperly; for, there was not the least appearance of mist or fog, or thickness of atmosphere; on the contrary, the air seemed uncommonly clear.”

As K. D. Billinghurst observed in his 1955 essay  “Abnormal refraction, South African waters,” in the Marine Observer 25, 100–101:

 “. . . what at first appeared to be a fog bank proved to be a mirage.  With the coastline on the starboard side, distant 15 miles, a dark-blue mass, having every appearance of land with undulations as of hills, was seen on the port bow from about 4 points to 1 point off the bow where it faded into a white band above the horizon”. . . the smoke from these whalers and from our own ship did not rise above mast height, but flattened out and hung in the atmosphere in a great band about 100 ft above sea level.”

Similarly, P. Day, P. C. Dyer, and R. P. Swinney, in their 1982 essay “Abnormal refraction, Tasman Sea”, published in the Marine Obs. 52, 26–27, stated:
 “Initially an apparent line of haze or mist was observed, extending from the horizon to an altitude of 0° 10′ – 0° 13′ and presenting a false horizon. The ship’s funnel smoke was then observed trapped on a level with this, indicating an inversion . . . “

And in his essay “Abnormal refraction, Western North Atlantic,” published by J.J. Gomez in Marine Observer 35, 122 (1964), he says:

 “. . . a layer of haze, dark grey in colour and with a clearly defined upper surface, was seen all round the horizon. One ship appeared to be completely inverted and an iceberg which was not visible to the naked eye, seemed to be hanging upside down from the top of the layer.”

In the remarkable thirteenth-century manuscript known as the ‘King’s Mirror’, which contains accounts of Iceland and Greenland that are rational and accurate to a degree not usually found in writings of the time, there is evidence that the Vikings called these apparent fog banks ‘hafgerdingar’ or ‘sea hedges’:

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13th Century Manuscript of ‘The King’s Mirror’. The manuscript belongs to The Arnamagnæan Collection. ©The Arnamagnæan Institute

“Now there is still another marvel in the seas of Greenland, the facts of which I do not know precisely. It is called ‘sea hedges’ [hafgerdingar], and it has the appearance as if all the waves and tempests of the ocean have been collected into three great heaps, out of which three billows are formed. These hedge in the entire sea, so that no opening can be seen anywhere; they are higher than lofty mountains and resemble steep, overhanging cliffs.”

In his book about his whaling voyage to the Greenland Sea in 1822, William Scoresby Jr (1823: 163) provided fascinating descriptions of many mirages. On 16 July, when he calculated his position to be 72°33 N, 19°9 W, his ship was in the Greenland Sea about 100 km (62 miles) off the Greenland coast. In his account of ‘the optical phenomena of unequal refraction,’ he described a striking mirage that he observed that day:

‘At one period (about 10 PM of the 16th) the phenomenon was so universal, that the space in which the ship navigated seemed to be one vast circular area, bounded by a mural precipice, of great elevation, of basaltic ice.’ On page 169 of his book, he summarised several of his observations: ‘. . . it [the sea ice] presents the appearance of a vast amphitheatre, which is so disposed, that every observer, whatever may be his position, imagines himself to be in the centre of it.’

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William Scoresby

Although Scoresby appears to have had no knowledge about the King’s Mirror, his description immediately brings to mind the hafgerdingar.

As J. Pilling and D. L. Smith observed in their essay “Abnormal refraction, South Australian waters”, published in the Marine Observer 34, 18–19 (1964):

 “. . . the horizon appeared to become raised above the sea and separated from it by an indistinct misty band. . . the  appearance was that of a bank of fog.”

Here’s another example of a mirage appearing like a slight haze on the water:

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In this photograph a superior mirage appears like a haze on the horizon © Wim van Bochoven 2002, the Netherlands.

This photograph was taken in Norway in the Spring, the same season and similarly high latitude in which Titanic sank and when superior mirages are most common: the water still has the chill of winter, but the air is warming up; Wim noted when he took this picture that it had been warm during the day and Titanic’s survivors noted that the weather had been sunny on the day of the collision.  The air was also calm, as it was the night the Titanic sank: no wind to mix the cold air next to the ocean with the warm air overlying it.

I hope by blogging chapters from my book, A Very Deceiving Night, it will contribute to the ongoing discussions regarding the atmospheric conditions on the night of the tragedy and the true causes of the disaster. At the moment, the book is only available as an e-book. If you wish to purchase it then you can do so in Amazon Kindle format here and other formats, including Apple, Kobo and Nook, here. Thank you.

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