Noctilucent Clouds - Night shining, polar mesospheric clouds
It's that time of year. Noctilucent clouds are visible in June but rare enough to cause excitement. These high ice crystal clouds can only be seen in the midsummer twilight. Once the sun comes out the light is too strong for these delicate, pale threads to be seen, they need the semi-darkness. Usually, cloud viewed in high latitudes, they were seen in mid-June 2018 in Norfolk and the Netherlands with brilliant displays over northern Britan and Northern Ireland.
WMO Cloud Atlas Definition ; Clouds resembling wispy cirrus but usually with a bluish or silvery colour; they stand out against the dark night sky well past summer sunset because they are in the mesosphere.
High up in the atmosphere, near the top of a layer called the mesosphere, the air is very cold with ice particles from May through the summer months (in the northern hemisphere). Around mid summer with the sun just below the horizon, there is enough light to illuminate the clouds but dark enough skies to contrast and see them. They are also called Polar Mesospheric Clouds (PMCs), night-shining clouds and look out for #NCL or #NCLnow for the next view
These clouds are studied closely as they are sensitive to changes in the upper atmosphere, giving clues for climate change research. There are suggestions that noctilucent clouds are being seen more often, as they are brighter, is that part of climate change with more CO2, CH4 and CFCs altering all layers of the atmosphere?
WMO "Noctilucent clouds are composed of very small water ice crystals formed on minute particles of dust, possibly of cosmic origin from micrometeors".