The skies over parts of Britain turned a soft shade of pink on Wednesday morning as the low sun shone through layers of widespread fog to produce the rare atmospheric treat.
Meteorologists at the Met Office said the fog formed when temperatures dropped overnight and issued a yellow warning across a large area of central and northern England where the fog would be slow to clear. The warning remained in effect until 10am.
Patches of particularly dense fog formed across the East Midlands and Cambridgeshire where poor visibility was expected to lead to difficult travel conditions.
Like clouds, fog is caused by tiny water droplets suspended in the air. It can appear pink because the water droplets scatter short wavelengths of sunlight – the blues and greens – more than the longer red wavelengths, allowing the red to dominate.
The pink colour is usually seen at the start and end of the day when the sun is low on the horizon and sunlight passes through more atmosphere than when it is higher in the sky.
A Met Office spokesperson said: “Fog is essentially a cloud at ground level made up of tiny water droplets. When the sun is low on the horizon, its light travels through more of the atmosphere. Shorter wavelengths are scattered out, leaving the longer red wavelengths to dominate. When this filtered light shines through fog, it gives the fog a pink or rosy hue.”
Despite the surreal appearance, it is nothing more than the physics of light playing out at sunrise and sunset.
“It’s important to note that pink fog is purely an optical effect,” the spokesperson said. “It does not indicate any unusual weather hazard beyond normal fog risks, such as reduced visibility.”
The phenomenon has been spotted in the UK before. In 2019, the early morning sky turned pink as fog formed across parts of south west England.
But Dr Claire Ryder, an associate professor at the University of Reading, said the effect was rare because multiple conditions had to be perfect for the pink colour to arise.
“This effect is caused by a reddish sunrise being ‘filtered’ by the fog. The sunrise produces the red light, by removing the bluer colours, and then the small fog droplets scatter the light more, dimming the effect, giving it a muted pink glow,” she said.
“It’s quite interesting and rare: you need the fog to occur at the exact sunrise or sunset time, and also for the fog to consist of a perfect thickness, or droplet concentration and droplet size, to get the right effect. Too thick a fog would block out all the light, and too thin a fog wouldn’t mute the sunrise colours very much.”
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