Pictured: Rare upside-down rainbow spotted in the UK

[Nostalgia]

If you look closely, just below the cloud you will notice the remnants of a "contrail", it is my bet that it is actually the contrail that is creating the rainbow.

But if contrails are just made up of water vapour and ice crystals just like clouds, then how come we don't see upside down rainbows all the time? Hmmm, that's a dilemma.
I love how the article below struggles to give us an explanation, yet totally misses the "contrail".
Er, HellooO.



It appeared in the sky for the briefest of moments.

A dazzling arc of psychedelic colour reminiscent of the Cheshire Cat's grin in Lewis Carroll's Alice in Wonderland.

But this is no fantasy or trick of the light, it is known as a circumzenithal arc. Seen here shimmering in the sky over Cambridge in the afternoon sunshine, it is often mistaken for a rainbow hanging upside down.

But unlike a rainbow, the sky has to be clear of rain and low level clouds for it to be seen.

Relatively rare in Britain, the arc only appears when sunlight shines at a specific angle through a thin veil of wispy clouds at a height of around 20,000 to 25,000 feet.

At this altitude the cirrus clouds are made of ice crystals, the size of grains of salt.

Meteorologists say the clouds must be convex to the sun with the ice particles lined up together in the right direction to refract the light.

This results in the sunlight bouncing off the ice crystals high in the atmosphere, sending the light rays back up and bending the sunlight like a glass prism into a spectrum of colour.

Renowned astronomer and writer Dr Jacqueline Mitton was lucky enough to capture the optical phenomenon on camera near her home in Cambridge last Sunday.

The 60-year-old who has a doctorate in astrophysics from Cambridge University said: 'I've never seen anything like it before - and I'm 60.

'The conditions have to be just right: you need the right sort of ice crystals and the sky has to be clear.

'It's quite surprising for this to occur somewhere like Cambridge, usually it is in places that are colder.

'We're not sure how big an area it was visible over, but it was certainly very impressive.'

According to Dr Mitton, the colours in the rainbow were intensified by the position of the sun, which was at the optimum spot in the sky of 22 degrees.

The vision was made even more dazzling by the presence of "sun dogs" - gleaming spots on a halo around the sun.

Dr Mitton added: 'It was just an amazing combination of factors that happened at the right time.'

Her husband Simon, 62, an astronomy writer, said: 'The circumzenithal arc is a quarter circle, pointing toward the setting sun.

'The "rainbow'" is much brighter and more concentrated than a rainfall rainbow.'

Rainbows are formed when sunlight is refracted in a raindrop.

But in a circumzenithal arc, the colours are in reverse order from a rainbow, with violet on the top and red at the bottom.

The arc usually vanishes quickly because the cirrus clouds containing the ice crystals shift their position.

Ice particles in high cirrus clouds occur all year round, but circumzenithal arcs are usually obscured by lower level clouds.

Circumzenithal arcs are so named as they go around the zenith - the point in the sky directly above the observer- rather than the sun.

A spokesman for the Met Office said: "Circumzenithal arcs are seen relatively rarely in Britain because they can only be seen at the right combination of atmospheric conditions.

'The height, depth and position of the ice clouds must be right as the cloud needs to be at a specific angle convex to the sun.

'Circumzenithal arcs actually occur quite commonly as these types of clouds occur throughout the year.

'But the vision is usually obscured by clouds underneath which means circumzenithal arcs are much rarer than rainbows and halos

'It is quite rare to see one as vivid as this. It depends on the position of the observer because its visibility can vary greatly, someone ten miles away would probably not be able to see it.'
http://www.dailymail.co.uk/news/arti...potted-UK.html

[Nostalgia]

Originally Posted by Nostalgia

Relatively rare in Britain, the arc only appears when sunlight shines at a specific angle through a thin veil of wispy clouds at a height of around 20,000 to 25,000 feet.

"Exhaust vapour trails or contrails usually occur above 8000 metres (26,000 feet). where the temperature is below -40°C (-40°F)."

[Nostalgia]

The vision was made even more dazzling by the presence of "sun dogs" - gleaming spots on a halo around the sun.

Here is one of my own photos that I took of a sundog in September 2003, notice the streaks of "contrails" that fill the sky.

[Nostalgia]

I took this video a couple of years ago, in it it you will see planes crossing the sky leaving thick contrails, but also, what you will notice is what looks like a second sun, to the right of the actual sun, which would be called a sun dog and is apparently rare to see.
I think that the sun dog is created by the refractory nature of the contrails.

Apologies for the shakyness of the camera, but holding a camera steady was not mentioned on the resume.

http://media.putfile.com/Two-Suns-in-the-Sunset

[Nostalgia]

GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L12814, doi:10.1029/2005GL022740, 2005

Do aircraft black carbon emissions affect cirrus clouds on the global scale?

J. Hendricks

DLR-Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

B. Kärcher

DLR-Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

U. Lohmann

ETH, Institut für Atmosphäre und Klima, Zürich, Switzerland

M. Ponater

DLR-Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

Abstract

Potential cirrus modifications caused by aircraft-produced black carbon (BC) particles via heterogeneous ice nucleation were studied with a general circulation model. Since the role of BC in cirrus cloud formation is currently not well known, hypothetical scenarios based on various assumptions on the ice nucleation efficiency of background and aircraft-induced BC particles were considered. Using these scenarios, the sensitivity of ice cloud microphysics to aviation-induced BC perturbations is studied. The model results suggest that cloud modifications induced by aircraft BC particles could change the ice crystal number concentration at northern midlatitudes significantly (10–40% changes of annual mean zonal averages at main flight altitudes), provided that such BC particles serve as efficient ice nuclei. The sign of the effect depends on the specific assumptions on aerosol-induced ice nucleation. These results demonstrate that, based on the current knowledge, significant cirrus modifications by BC from aircraft cannot be excluded.

Received 17 February 2005; accepted 18 May 2005; published 24 June 2005.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 1610 Global Change: Atmosphere (0315, 0325); 3311 Atmospheric Processes: Clouds and aerosols; 3337 Atmospheric Processes: Global climate models (1626, 4928).
http://www.agu.org/pubs/crossref/200...GL022740.shtml

Black carbon climate danger ‘underestimated’

Black carbon, a key component of soot, plays a much larger role in global warming than previously estimated, scientists have found.

They cite black carbon as the second largest contributor to global warming after carbon dioxide.

"We've got one more thing to worry about," says Veerabhadran Ramanathan, professor at the Scripps Institution of Oceanography at the US-based University of California at San Diego and co-author of the study.

"We thought it was mainly carbon dioxide emissions [contributing to global warming]. Now we know that there is another major culprit. Our finding adds to the complexity of the issue."

Black carbon is produced from the incomplete combustion of wood, biomass such as crop residues and fossil fuels.

Ramanathan, together with Greg Carmichael at the University of Iowa, United States, combined satellite data with aircraft and surface observations to paint a global picture of the warming effects of black carbon emissions.

Black carbon absorbs solar radiation, warming the atmosphere. The researchers calculated this warming effect as 0.9 watts per square metre, second to carbon dioxide's value of 1.66 per square metre.

But this is much higher than the 0.2–0.4 watts per square metre estimated by the UN Intergovernmental Panel on Climate Change.

Ramanathan told SciDev.Net that reducing black carbon emissions is a real possibility as the atmospheric lifespan of black carbon is short, "in the order of 10 days or less". As a result, the benefits will be reaped quickly.

"To cut down carbon dioxide emissions, we are talking about trillions of dollars," he says. "My feeling is black carbon is going to be 10–100 times cheaper. Black carbon emissions in Germany and the United Kingdom have come down by a factor of 2–3 in the last 30–40 years. This shows that we know how to do it."

Ramanathan is undertaking a study in India to look at the cost-effectiveness of biogas plants and encouraging the use of solar cookers instead of burning biomass in villages.

He is currently working with the Chicago Climate Exchange Commission to provide the villagers with carbon credits to sustain these new cooking methods.

A report building on Ramanathan's and Carmichael's analysis, assessing the impact of atmospheric brown clouds — formed from the mixing of black carbon with other aerosols — on China and India will be released by the UN later this year.

The study was published in Nature Geoscience.
http://www.climateactionprogramme.or...underestimated