Wednesday, April 26, 2017

Nacreous Munch



Weird clouds may have inspired ‘The Scream’: scientists

The Japan Times  AFP-JIJI  Apr 25, 2017

A visitor looks at Edvard Munch's painting 'The Scream' at the Munch Museum in Oslo in May 2008. | AFP-JIJI 

VIENNA – The psychedelic clouds in Edvard Munch’s iconic “The Scream” have alternatively been interpreted as a metaphor for mental anguish or a literal depiction of volcanic fallout.

On Monday, scientists hypothesized that the Norwegian painter’s inspiration may in fact have been rare clouds that form in cold places at high altitude.

The first version of “The Scream” was released in 1893. It depicts a dark humanlike figure clutching its head in apparent horror against the backdrop of a swirling, red-orange sky.

In 2004, American astronomers theorized that Munch had painted a sky brightly colored by particle pollution from the 1883 Krakatoa volcanic eruption.

But the new paper, presented at a meeting of the European Geosciences Union in Vienna, said he more likely depicted a rare sighting of “mother-of-pearl” clouds over Oslo.

A volcanic outburst does not account for the “waviness” of Munch’s clouds, Helene Muri, a researcher at the University of Oslo, told journalists in Vienna.

Furthermore, volcano-tinted sunsets tend to be common for several years after an outburst, “whereas Munch’s scary vision was seemingly a one-time experience, the way he described it in his journal,” she said.

In his diary, Munch wrote of the sky turning suddenly blood red.

Mother-of-pearl or “nacreous” clouds, require unusual conditions to form — very cold temperatures in the atmosphere, in a high altitude band of about 20-30 kilometers (12-19 miles).

They tend to appear at high latitudes in winter.

Because they are thin, these clouds are typically not visible during daytime, but before sunrise or after sunset.

“We do know that there were mother-of-pearl clouds in the Oslo area in the late 19th century,” said Muri.

At least one scientist documented the phenomenon and wrote “they are so beautiful you could believe you are in another world,” she added.

Similar sightings of nacreous clouds over southeast Norway in 2014, and their striking resemblance to Munch’s painting, is what sparked the latest research.

“Edvard Munch could well have been terrified when the sky all of a sudden turned ‘bloodish red,’ ” the researchers concluded.

“Hence, there is a high probability that it was an event of mother-of-pearl clouds which was the background for Munch’s experience in nature, and for his iconic ‘Scream.’ ”

Muri conceded the latest was but “another hypothesis.”

“There are other hypotheses. But of course, we are natural scientists, we tend to look for answers in nature, whilst the psychologists have suggested it was inner torment that made Munch paint ‘The Scream.’ “
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So what about these "nacreous clouds"?  From: Wikipedia


Polar stratospheric clouds or PSCs, also known as nacreous clouds (/ˈnkr.əs/, from nacre, or mother of pearl, due to its iridescence), are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 meters (49,000–82,000 ft). They are best observed during civil twilight when the sun is between 1 and 6 degrees below the horizon as well as in winter and in more northerly latitudes.

 
 They are implicated in the formation of ozone holes. The effects on ozone depletion arise because they support chemical reactions that produce active chlorine which catalyzes ozone destruction, and also because they remove gaseous nitric acid, perturbing nitrogen and chlorine cycles in a way which increases ozone destruction.

Formation

The stratosphere is very dry; unlike the troposphere, it rarely allows clouds to form. In the extreme cold of the polar winter, however, stratospheric clouds of different types may form, which are classified according to their physical state and chemical composition.

Due to their high altitude and the curvature of the surface of the Earth, these clouds will receive sunlight from below the horizon and reflect it to the ground, shining brightly well before dawn or after dusk.

PSCs form at very low temperatures, below −78 °C (−108 °F). These temperatures can occur in the lower stratosphere in polar winter. In the Antarctic, temperatures below −88 °C (−126 °F) frequently cause type II PSCs. Such low temperatures are rarer in the Arctic. In the Northern hemisphere, the generation of lee waves by mountains may locally cool the lower stratosphere and lead to the formation of PSCs.



Forward-scattering of sunlight within the clouds produces a pearly-white appearance. Particles within the optically thin clouds cause colored Interference fringes by diffraction. The visibility of the colors may be enhanced with a polarising filter.



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