Nacreous clouds are fundamental to the creation of the ozone hole over Antarctica and are rarely seen from the UK. The clouds form over both polar regions at heights of around 10 to 20km. They are usually visible during civil twilight – the denser cloud has beautiful pearly coloured margins and is quite bright, but there is also a diffuse form that appears like thin stratocumulus cloud (a normal form of quiet weather cloud), but is much higher. As a consequence the stratospheric clouds remain relatively bright long after normal stratocumulus would have turned dark at sunset. This winter has seen an unusually cold Arctic stratosphere, and at the start of February the “polar vortex” with the coldest air became very elongated and reached down to the UK.
Civil twilight ended at 17.22 local time on 2 Feb. Here’s a shot timed at 17.14 with my basic 10-year-old phone camera of the diffuse form of clouds. These appeared out of an otherwise cloudless sky as the illumination caught them right.