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The Nacreous clouds or Polar Stratospheric clouds (PSC) are a rare phenomena only visible in the mid winter in the polar regions. They are formed like any other clouds, but at very high altitudes, 15,000 - 25,000 meters (49,000-82,000 ft) and get the rainbow like colours when the sun hits them before rising above the horizon. The ice crystals in these clouds are hit by the light of the rising sun at dawn, when it is 1-6 degrees below the horizon at civil twilight. PSC are formed at very low temperatures, below -78 degrees Celsius (-108 deg. F) and even though the stratosphere is very dry the clouds may form when the conditions are right. The main type of PSC is made up of supercooled water droplets and nitric acid and has been linked to formation of ozone holes. The other type is made of ice crystals only and is not harmful to the atmosphere.

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I have managed to capture PSC a few times in Iceland, maybe 5-6 times in the last 10 years, which indicates how rare they are, or maybe just how lazy I am in the winter. Of course there have to be good conditions on the ground, not heavy clouds, raining or snowing as often is in the winter. The weather forecast is helpful if you are planing to try your luck with PSC, and going out around one hour before sunrise when the sky is predicted to be clear. Shooting with a medium telephoto lens, such as 24-105 or 70-200 mm will give good result, and using a polarising filter can enhance the colours. I also underexpose to get the most out of the shots, as the PSC are often much brighter than the sky around them.

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In some instances the PSC are still visible after the sun rises, like on December 28 2020 when I captured most of the photos here. That is even more rare and very beautiful to see. I was on a photo shoot in Reykjavik early in the morning that day and captured a few shots of PSC over Reykjavik and over Hveragerði in the south the morning before. Also when I got back home to Selfoss in the middle of the day, well before sunset when I also captured a few videos of the Nacreous clouds.

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Every time that I have seen these clouds is from mid December till end of January which is the coldest part of winter, so that could be one more reason to visit Iceland when the day is shortest. Sunrise in mid December is around 11:00 am and sunset at around 3:30 pm here in Iceland, so plenty of time to photograph Northern lights and Nacreous clouds - if you are lucky :-)

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