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Ghostly Brocken spectre floats over Scotland fog bank

Climbers captured the eerie scene as their shadows were cast onto a thick blanket of fog and surrounded by rings of light

A Brocken specter, as seen from a Scottish mountaintop. (Toby Stead)

When you’re as avid of a hiker and mountain climber as Toby Stead is, odds are you’ve seen a lot of things. But what Stead witnessed while hiking over the weekend in Scotland was an extra-special treat that was as mystical as it was mesmerizing.

Stead encountered the ghostly atmospheric phenomenon known as a Brocken spectre, when his shadow was cast onto an underlying bank of fog and surrounded by concentric circles of colorful light. The phenomenon draws its name from the Brocken peak in the Harz highlands in Germany, where it is commonly observed.

Scotland’s topography, proximity to the ocean and erratic winter climate make it suited to the phenomenon (see examples from BBC and the Scotsman).

Stead’s hike started gloomy, with fog, mist and cool temperatures, but it cleared up and warmed as he summited one of Scotland’s many mountains outside Glasgow.

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Of his trek, Stead wrote in an email that “Glasgow (and by the looks of things everywhere else) [had] been very cold and foggy, but above a certain altitude, around 400 [meters], the air [was] much warmer, and there was no wind to stir everything up.” He said that only once he and his companion, Charlie Smith, descended closer to the shallow cold layer did they notice the unusual spectacle. They had their backs to the sun and their shadows in front of them.

The images depict the photographers’ elongated shadow projected onto a thick blanket of stratus, or fog, below. In the distance, it is obvious just how sharp the interface between air masses is, a razor-thin line dividing mountains from a cloak of whiteness.

The Brocken spectre forms opposite the sun and is made up of a bright circle surrounded by rings of color, known as a glory. The central bull’s eye of luminance is formed by light reflected inside water droplets, converging from the perspective of the viewer. Colors emerge when water droplets scatter the light backward.

According to Atmospheric Optics, a website that specializes in optical phenomena, some sunlight skims along the surface of a spherical raindrop before being bent inside it, ultimately beamed almost directly back to the observer. Different wavelengths, or colors, of light are refracted (bent) at acutely different angles. That splits white light into its component colors.

Glories are also visible from airplanes, too. Generally speaking, a person can only see a glory around his or her own shadow. Much like with rainbows, every person witnesses their own unique glory.

We can turn to a weather balloon sounding taken from Lerwick in northern Scotland at the time of Stead’s hike for more insight into the environmental setup. An extremely robust inversion, or increase in temperature with height, can be seen. The black line on the left represents dew point, or the amount of moisture in the air, and the right line demarcates temperature. When the two lines touch, the air is saturated and the natural result is fog or precipitation.

We can see that, at about 700 meters (approximately 2,300 feet) above sea level, the air reached full saturation. That brought fog and mist. There may have even been some freezing fog, with temperatures around minus-1.8 degrees Celsius (28.6 Fahrenheit).

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Then a layer of unbelievably dry air is present immediately overhead. By 916 meters (about 3,000 feet), dew points drop to around minus-40 degrees (minus-40 Fahrenheit) — meaning there’s virtually no water in the air. To go from full saturation to bone dry in 215 meters (700 feet) is extremely rare.

Temperatures continue to warm with height through about 1,830 meters (6,000 feet), at which point the air is around 4 degrees Celsius (39 Fahrenheit). Ordinarily temperatures tend to fall about 6.5 degrees Celsius (12 Fahrenheit) per 1,000 meters (3,200 feet) as one climbs in the atmosphere. Instead they warmed at a rate greater than 10 degrees (18 Fahrenheit) per 1,000 meters.

The strange setup allowed Stead the perfect opportunity to witness a curious phenomenon few get to experience. It’s yet another reminder that the atmosphere can deliver beauty and surprise when we least expect it.