OPOD - SuperiorSuperior Mirage

Last updated on September 16, 2023

OPOD - Superior Superior Mirage: A Fascinating Optical Phenomenon

Have you ever witnessed a mind-bending mirage where a ship appears to be sailing upside down on a lake? This captivating phenomenon is known as a "superior" superior mirage. It occurs when dense, cold air near the surface of a body of water is overlaid by less dense, warmer air. The interaction between these air layers causes light rays to bend and create a stunning optical illusion.

The Science Behind the Mirage

When light rays pass through the boundary between the colder and warmer air layers, they are refracted, or bent, along curved paths. The curvature of the rays is most pronounced where they cross the strongest vertical temperature gradient. In the case of a superior mirage, the rays tend to curve concave towards the sea level line, causing the second image to appear above the actual object being miraged.

To understand this phenomenon better, let's examine the path of different rays from a ship sailing on Lake Superior:

• Ray 'a' originates from the ship's mast and passes through only cold air, resulting in minimal deviation. Consequently, no mirage is observed, and the lower image of the ship appears unaffected.
• Ray 'b' grazes the boundary between the cold and warm air layers and is refracted downwards. This refraction causes the ray to appear as if it is coming from a point above the true position of the ship. The miraged image of the ship is inverted and located above the ship itself.
• Ray 'c' originates from the ship's hull and penetrates deeper into the cold/warm boundary due to its increased angle to the sea. As a result, it is refracted more strongly than ray 'b'. Consequently, this ray appears to come from a point higher than that of ray 'b', creating an additional miraged image above the inverted one.

Factors Influencing the Mirage

The depth of the temperature inversion layer plays a significant role in determining the characteristics of the mirage. In cases where the inversion layer is deep, there may even be a third image above the inverted one, this time appearing right-side up. However, when the inversion layer is relatively shallow, as observed in the Lake Superior mirage, only a portion of the ship is mirrored upside down above the real ship.

Moreover, it is worth noting that the boundary of the inversion layer can occasionally be seen miraging the sea itself, creating a captivating visual spectacle. This occurrence adds an additional element of intrigue to an already mesmerizing phenomenon.

Capturing the Mirage

Photographers and enthusiasts are often drawn to superior superior mirages due to their striking visual appeal. The shimmering mirage near the horizon, coupled with the inverted image of a ship sailing on water, presents an ethereal and dreamlike scene. To capture this phenomenon, it is essential to set up a camera on a tripod to ensure stability and take multiple stills or video segments as the miraged object moves through the mirage.

Conclusion

The superior superior mirage is a captivating atmospheric optics phenomenon that showcases the fascinating interplay between air layers of differing densities. Through refraction, light rays create an optical illusion where objects appear inverted and above their actual position. The depth of the temperature inversion layer and the angle at which the rays pass through it influence the characteristics of the mirage. Whether you are lucky enough to witness this enchanting spectacle firsthand or admire it through photographs, the superior superior mirage never fails to captivate and leave us in awe of nature's wonders.

'Superior' Superior Mirage

A ship topped by an upside down clone sails on Lake Superior.

Imaged by Mary Lynn Skirvin Johnson. "We were driving along the shore of Lake Superior in Keweenaw County, Michigan and noticed a shimmering mirage near the horizon and saw that a large freighter was heading right for it. I stopped at Great Sand Bay, set up my camera on a tripod and took several stills as well as a few video segments as the boat moved through the mirage. The crane and other structures are seen nicely inverted above the deck."

Image ©Mary Lynn Skirvin Johnson, shown with permission

This is a superior mirage, so named because the second image is above the miraged object.

The mirage is the result of dense cold air near to the lake surface topped by less dense warmer air.

Light rays passing between the colder air and the upper warm air are refracted to follow curved paths. The rays tend to be concave towards the sea level line i.e. initially u.upward rays tend to curve downwards again. The ray curvature is greatest where the rays cross the strongest vertical temperature gradient.

At left the ray 'a' from the ship's mast passes through only cold air and is hardly deviated - the lower image of the ship appears it would be with no mirage taking place.

Ray 'b' from the same point on the ship grazes the boundary between the cold and warm air layers and is refracted downwards - refracted rays always curve towards the colder and denser air. To the eye ray 'b' appears to be coming from a point above the real position of the ship.

Now look at one of the rays from the ship's hull - ray 'c'. Its increased angle to the sea causes it to penetrate deeper into the cold/warm boundary and it is refracted more strongly. To the eye it appears to come from a point higher than that of ray 'b'. The miraged image of the ship is inverted and above the ship itself.

When the temperature inversion layer is deep there is even another image above the inverted one, this time the right way up. The Lake Superior mirage, above, had a relatively shallow inversion layer and only part of the ship is miraged upside down above the 'real' ship. The boundary of the inversion layer can be seen elsewhere above the horizon as it momentarily mirages the sea itself.

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Reference Atmospheric Optics

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