UPDATE:

For the second day in a row, sky watchers are reporting an outbreak of polar stratospheric clouds (PSCs) around the Arctic Circle. Unlike normal grey-white clouds, which hug Earth's surface at altitudes of only 5 to 10 km, PSCs float through the stratosphere (25 km) and they are fantastically colorful. Truls Tiller photographed these over Tromsø, Norway, on Dec. 16th:

photo Truls Tiller 

"Here the sun is gone for now," says Tiller, "but this beautiful view makes the winter darkness nice to be in as well. The picture was taken at 10.30 am, in the middle of the 'day.'"

Also known as "nacreous" or "mother of pearl" clouds, the icy structures form in the lower stratosphere when temperatures drop to around minus 85ºC. High-altitude sunlight shining through tiny ice particles ~10µm across produce the characteristic bright iridescent colors by diffraction and interference. Once thought to be mere curiosities, some PSCs are now known to be associated with the destruction of ozone.

"Nacreous clouds far outshine and have much more vivid colours than ordinary iridescent clouds, which are very much poor relations and seen frequently all over the world," writes atmospheric optics expert Les Cowley. "Once seen they are never forgotten."
Bron:http://www.spaceweather.com/ | Gewijzigd: 31 januari 2017, 15:52 uur, door Joyce.s

Polar stratospheric clouds over the UK:
An outbreak of polar stratospheric clouds (PSCs) is underway--but not around the poles. Sky watchers are reporting the beautifully-colored clouds over the UK. David Porter photographed this specimen on Jan. 29th from his home in Turriff, Aberdeenshire:

photo  David Porter

"I saw it just before sunrise," says Porter. "The cloud was colorful and highly reflective." Rob Powell of Stonehaven, Scotland, saw them, too. "It was a lovely sunrise," he says.

Also known as "nacreous" or "mother of pearl" clouds, icy PSCs form in the lower stratosphere when temperatures drop to around minus 85ºC. High-altitude sunlight shining through tiny ice particles ~10µm wide produce bright iridescent colors by diffraction and interference. Once thought to be mere curiosities, some PSCs are now known to be associated with the destruction of ozone.

"Nacreous clouds far outshine and have much more vivid colours than ordinary iridescent clouds, which are very much poor relations and seen frequently all over the world," writes atmospheric optics expert Les Cowley. "Once seen they are never forgotten."
Bron: http://www.spaceweather.com/ | Gewijzigd: 31 januari 2017, 15:53 uur, door Joyce.s

OZONE HOLE FORMS OVER THE UK: 
For the past week, sky watchers in the UK have witnessed a rare apparition of polar stratospheric clouds (PSCs). Normally restricted to the Arctic Circle, the fantastically colorful clouds have appeared over the British Isles almost every day since Jan. 31st. Colin Fraser photographed the display over Edinburgh, Scotland, on Feb. 2nd:

photo Colin Fraser 

PSCs form in the lower stratosphere when temperatures drop to a staggeringly-cold -85ºC. High-altitude sunlight shining through tiny ice particles ~10µm wide produce bright iridescent colors by diffraction and interference.

But there is more to PSCs than ice. Some polar stratospheric clouds contain very small droplets of naturally occurring nitric and sulphuric acids. These droplets destroy ozone. Indeed, atmospheric optics expert Les Cowley points out that a temporary ozone hole has formed over Ireland and the UK. It is the blue patch in this Feb. 1st ozone map from NASA's Arctic Ozone Watch:

"The acid droplets destroy the stratospheric ozone layer that protects us from harmful solar ultra-violet rays," says Cowley. "They catalyse unreactive forms of man-made chlorine into active free radicals (for example ClO, chlorine monoxide). The radicals destroy many ozone molecules in a series of chain reactions.."

This outbreak of PSCs is truly unusual. "Prior to this outbreak I have seen PSCs over the UK only twice in the last 20 years!" says Cowley. "This episode is exceptional at such low latitudes.  If it goes on any longer my camera will be worn out."
Bron: http://www.spaceweather.com/ | Gewijzigd: 31 januari 2017, 15:55 uur, door Joyce.s

Polar stratospheric clouds

The stratosphere is a relatively clear layer of Earth's atmosphere, almost always cloud-free. Almost always. Yesterday, researchers at Argentina's San Martín Base spotted a bank of fantastically colored clouds floating in the stratosphere above the Antarctic Peninsula:

photo  photographer "Marcelo,

"There were the biggest stratospheric clouds we've seen so far this year," says photographer "Marcelo," who is working at the Base this winter. "It was a colorful spectacle to begin the day."

These are called "Polar Stratospheric Clouds" (PSCs). They form in the lower stratosphere when temperatures drop to around minus 85º C. This explains why they are rare; even at the poles, such low temperatures are hard to achieve. High-altitude sunlight shining through tiny (~10µm) ice particles in PSCs produce bright iridescent colors by diffraction and interference. Once thought to be mere curiosities, some PSCs are now known to be associated with the destruction of ozone.

Apparitions of these clouds often persist for days. Stay tuned for more sightings from the frozen continent.
Bron: http://www.spaceweather.com/  | Gewijzigd: 31 januari 2017, 15:58 uur, door Joyce.s

BEST EVER? POLAR STRATOSPHERIC CLOUDS:
 Around the Arctic Circle, observers are reporting an outbreak of polar stratospheric clouds (PSCs). "Yesterday, Feb. 13th, the sky was filled with their brilliant colors from sunrise to sunset," says Mia Stålnacke, who sends this picture from Kiruna, Sweden:

©Mia Stålnacke
These clouds are newsworthy because normally the stratosphere has no clouds at all. Home to the ozone layer, the stratosphere is arid and almost always transparent. Yet, Stålnacke says, "we've been seeing stratospheric clouds very often this winter and last." 


According to multiple longtime residents of the area, the Feb 13th display was exceptional. "Everyone I spoke to agrees it was the best they had ever seen," says Chad Blakley, who operates the Lights over Lapland tour guide service in Abisko, Sweden.


"I've been living here all my life (33 years)," says Stålnacke. "I definitely feel that these clouds are appearing more often then they used to. I remember seeing them a few times/year since I was a kid, but these last couple of years we've had them much more often--sometimes for almost a week straight. Others seem to feel the same way; I see local groups on Facebook flooded with photos of PSCs and comments on how often they're appearing now."

"The clouds were all over Finland, too," says Matti Helin who took this picture on Feb. 13th:

© Matti Helin 
What's going on up there?

PSCs are a sign of very cold temperatures in the stratosphere.  The clouds are made of ice. Indeed, that is the source of their remarkable color: High-altitude sunlight shining through tiny ice particles ~10µm across produce a bright iridescent glow.  For ice crystals to form in the very dry stratosphere, temperatures must drop to around -85º C.

Once thought to be mere curiosities, some PSCs are now known to be associated with the destruction of ozone. Indeed, an ozone hole formed over the UK in Feb. 2016 following an outbreak of ozone-destroying Type 1 PSCs. 


To investigate these clouds further, Spaceweather.com and the students of Earth to Sky Calculus will travel to Abisko Sweden for a week in March 2017.  We plan to launch a series of space weather balloons into the Arctic stratosphere, measuring temperature, air pressure, and ambient radiation.  If PSCs are present, our sensors will pass directly through them, and our cameras can photograph the colorful clouds at point blank range. Stay tuned!
Bron: http://spaceweather.com/

DAYTIME AURORAS? NO. POLAR STRATOSPHERIC CLOUDS: 
On Feb. 13th, something amazing happened in the stratosphere over the Arctic Circle. Normally, the air 60,000+ feet above Earth's surface is dry and utterly transparent.  On the eve of Valentine's Day, however, the Arctic stratosphere filled with a gossamer haze of crystalline ice, and when sunlight hit the freezing crystals, the sky filled with clouds of intense iridescent color.

"Our guests referred to the clouds as 'daytime auroras,'" reports Chad Blakley, who operates the Lights over Lapland tour guide service in Abisko, Sweden. One of them, Champ Cameron (@champcameron on Instagram), snapped this picture of the display:

©Chad Blakley
"Champ was participating in our Sami And Reindeer Experience outside of Abisko yesterday afternoon," explains Blakley. "The roads were very icy due to a freak rain storm and warm weather (+9 degrees C) so we nearly canceled the trip. But we heard that there were incredible clouds in the sky so we chose to brave the weather and push on."

Good thing. They witnessed an exceptional display of polar stratospheric clouds (PSCs). PSCs are a sign of very cold temperatures in the stratosphere. For ice crystals to form in the normally arid stratosphere, temperatures must drop to around -85º C. So while it was strangely warm on the ground below, it was incredibly cold up above.  

Longtime observers say PSCs are becoming more common and more intense. "I've been living here all my life (33 years)," says Mia Stålnacke of Kiruna, Sweden, who also photographed the colorful outbreak. "I definitely feel that these clouds are appearing more often then they used to. I remember seeing them a few times/year since I was a kid, but these last couple of years we've had them much more often--sometimes for almost a week straight. Others seem to feel the same way; I see local groups on Facebook flooded with photos of PSCs and comments on how often they're appearing now." 

"Our bus driver, a longtime resident of the area, described it as the best PSC display he had ever seen," relays Blakley. "We were overwhelmed by the natural beauty." The clouds were so intense, they remained visible even after the sun set:

"We saw these clouds all day long, and they continued into the night," says photographer Lars Lehnert of Abisko, Sweden. " I've never seen anything quite like it."

Once thought to be mere curiosities, some PSCs are now known to be associated with the destruction of ozone. Indeed, an ozone hole formed over the UK in Feb. 2016 following an outbreak of ozone-destroying Type 1 PSCs.

To investigate these clouds further, Spaceweather.com and the students of Earth to Sky Calculus will travel to Abisko Sweden for a week in March 2017.  We plan to launch a series of space weather balloons into the Arctic stratosphere, measuring temperature, air pressure, and ambient radiation.  If PSCs are present, our sensors will pass directly through them, and our cameras can photograph the colorful clouds at point blank range. Stay tuned!
Bron: http://spaceweather.com/