Category Archives: polar stratospheric clouds

Norway iridescent foehn clouds

On February 6, 2011, Dirk Steinborn observed these beautiful iridescent foehn clouds in Favang (about 1-hour-drive north of Lillehammer, Norway). The photographs were taken between 14 and 15 hours CET. The observer supposes: “Probably there weren´t any mother-of-pearl clouds. It is cirrus, but also some medium level clouds had a reddish colour.”

More pictures: 123456.

Unusually bright twilights over Western Europe

Between February 17 and February 20, 2008, large parts of Western Europe witnessed a seriesof unusually bright morning and evening twilights.

A few minutes after a quite normal sunset, the western skies began to burn in a strange yellow light which was bright enought to illuminate the landscape and giving a quite unreal touch to houses and trees.
Some minutes later, the yellow light in the west became surrounded by a brownish rim, turning into purple within some minutes. The yellow part of the sky slowly shrank towards the horizon, turning into orange and later into red and crimson. Some observers also reported of a dark, brownish-red light in the east which surrounded the whole horizon reaching up to 10° high.

The strange lights and colours in the sky were visible for up to about one hour after sunset. A similar “light-show” also appeared in the morning, starting with a crimson light over the eastern horizon and ending with the bright yellow light short before sunrise. The yellow illumination of the landscape could even be perceived through layers of low clouds (stratus) in some areas.

The phenomenon was reported from the British Isles, Scandinavia, The Netherlands and Germany, and there are even reports of unusual twilight observations from northern Spain.

These in some cases weird-looking twilights were probably caused by an outbreak of polar stratospheric clouds (PSC). These form at temperatures below -78°C in the stratosphere, at an altitude of about 20 – 25 km above the ground.
Soundings made at several stations showed that temperatures in the stratosphere really were unusually low over western Europe; up to -87°C (De Bilt) were measured, the lowest since measurements began in the 1980s. This makes the formation of PSC over a large area possible. Some photographs also show faint structures in the light, giving hints that they actually were caused by PSC.

Polar stratospheric clouds have never before been observed so far south. Normally, they can only be seen from Scandinavia, Canada and Alaska. Only in 1999 there was a confirmed observation of PSC from northern Germany.

Authors: Peter Krämer, Bochum & Claudia Hinz, Brannenburg

Mother-of-pearl clouds in Finland

A period of westerly tropospheric flows in Scandinavia is continuing to provide occasions of Mother-of-pearl (MoP) clouds to Finnish observers. Several MoP displays have been observed just before the Christmas at different locations, in particular in Central and Northern parts of Finland, but also at the Southern coast. The photograph taken by Mauri Laitinen in Kuopio, Eastern Finland, shows the beautifully coloured details of the afternoon display of 23rd December.

MoP clouds are seen a number of times each winter in Finland, but displays as bright as this one are fairly rare.
Usually the MoP clouds are related to stratospheric temperature colder than -80°C.

Author: Reima Eresmaa

Mother-of-pearl clouds over Colorado?

Caleb Jones took this photo in Estes Park, Colorado (USA) on 28 October, around 3:10pm local time. The weather had been mostly clear on this day. These clouds were relatively far from the sun, and the vivid iridescent colors seem to be caused by very small droplets that polar stratospheric clouds have. But the edges of the wave cloud look more like regular mid-level waveclouds.

The 00 UTC 29 October sounding of Denver doesn”t show unusually strong winds at high altitude, at 40 to 50 kts from the NW. In fact the entire troposphere seems rather dry on that particular sounding for lenticular clouds to occur.

I do not think this was caused by a missile launch either, considering the lenticular shape of the clouds.

I am wondering if these could be stratospheric clouds, or just some quite unusual appearance of lenticular mountain wave clouds. I received another report from someone else in Colorado who also took images, and am waiting for her approval to post them here as well.

Author: Harald Edens

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