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Dublin: 12 °C Sunday 15 September, 2019
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What causes this beautiful phenomenon seen around Ireland this week?

The phenomenon was spotted across the country this

Source: Bren Whelan/YouTube

EARLIER THIS WEEK, many people across Ireland began spotting rare ‘rainbow clouds’ high in the morning sky.

People were sharing photos of the multicoloured phenomenon from a number of parts of the country.

Bren Whelan of Wild Atlantic Way Rock Climbing managed to go a step further and captured a timelapse of the rainbow clouds in the skies about Lough Foyle in Donegal.

The video shows denser clouds underneath the rainbow clouds as they pass below with the rainbow clouds remaining bright above.

The coloured skies caused wonder and confusion among the people who saw them, but what exactly causes them?

Much like rainbows, the colours are caused by the diffraction of light.

weather 3 Source: Twitter/HurricaneArt

As Jessamyn Fairfield of City of Physics Dublin explains, diffraction is an optical process that occurs when light passes from air into a medium like water and bends because the properties of water are different than the properties of air.

Because different colours of light bend differently, we get the splaying of different colours like a prism.

In the case of rainbows the light is diffracted through droplets of water, but in rainbow clouds it occurs when the light passes through frozen crystals high up in the atmosphere.

The rainbow clouds, or nacreous clouds, can be 15km to 25km high in the atmosphere and are so thin and frozen they are almost like a lens.

As Fairfield explains, it’s because the there’s so little moisture up there:

These conditions are more easily met by clouds which are very high up in the stratosphere, because the stratosphere is very dry and rarely supports clouds, but the clouds which do form there are likely to be thin and wispy.

Read: A beautiful rare weather phenomenon brightened up this St. Brigid’s Day morning >

Read: The weather is getting weirder. There’s a hurricane FIVE MONTHS before hurricane season >

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About the author:

Rónán Duffy

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