Nacreous, polar stratospheric clouds, Donegal, Ireland

Nacreous Clouds over Ireland

These images by Daragh McDonough at Donegal, Ireland were taken this morning 1st February '16. The clouds shine their iridescent filmy colours into the dawn brightening sky.

Nacreous clouds, polar stratospheric clouds typeII, are exceeding rare at such low latitudes. They were expected, however, because stratospheric temperatures over Ireland and UK are very low and forecast to remain so for a few days. If you are in Ireland or UK look out for them this week before dawn and after sunset. There are even reports of possible daylight sightings.

Images ©Daragh McDonough, shown with permission

Nacreous clouds are arguable the planet's rarest.

They occur mostly at high latitudes, Scandinavia and Iceland but once every few years make forays further south.

They are 15 - 25 km high in the lower stratosphere. Compared with other PSCs (polar stratospheric clouds) they are composed of benign ice crystals. Other PSCs have nitrogen acids that catalyse the destruction of protective ozone.

Nacreous clouds form at temperatures of -85 Celsius and below and (like now!) are often associated with very strong gusting surface winds that possible help transport the necessary water into the stratosphere.