mysterious glowing clouds

[Lt_Ripley]

Satellite snaps first images of mysterious glowing clouds

23:17 29 June 2007

NewScientist.com news service

David Shiga

Veres Viktor of Budapest, Hungary, took this image of noctilucent clouds on 15 June 2007, one of the first ground-based sightings of the season (Image: Veres Viktor)A new satellite has captured its first views of enigmatic glowing clouds whose proliferation may be linked to climate change.

NASA launched the Aeronomy of Ice in the Mesosphere (AIM) satellite on 25 April on a mission to investigate "night-shining" or noctilucent clouds. These clouds float 80 kilometres above the ground and are made of tiny ice crystals. Because they are so high up, the Sun still reaches them and makes them glow after sunset and before sunrise, when the ground is in darkness.

The clouds have been observed since the 1800s, but in recent years they have brightened and grown more numerous. They were first observed above Earth's polar regions, but have now spread to latitudes as low as 40°. Some scientists suspect their proliferation is related to increasing greenhouse gases, which can actually cause the upper reaches of the atmosphere to cool.

Now, the AIM satellite has inaugurated a new era in noctilucent cloud research, obtaining its first views of these ghostly structures.

The satellite spotted its first noctilucent clouds on 25 May. Since then, the clouds have become more numerous and have spread to lower latitudes (see map at right of the clouds' distribution on 11 June).

Low temperatures

AIM has observed the pattern of noctilucent clouds around the north pole rotating over time. Russell suspects this may be due to areas of especially low temperature moving around rather than the clouds themselves moving. Temperatures where the clouds form hover at about -140° C.

Some researchers suspect the increase in the clouds seen in recent years could be due to human activity. Carbon dioxide absorbs energy in the upper atmosphere as well as radiation leaving the Earth's surface and then reradiates it very efficiently.

About half of that energy returns to the Earth's surface, causing warming. But because the carbon dioxide helps radiate energy away from the upper atmosphere, there is a net cooling there.

Human activities

"Temperature certainly is one plausible explanation for why we're seeing more of the clouds and at lower latitudes and brighter," AIM chief scientist James Russell III of Hampton University in Hampton, Virginia, US, told New Scientist.

He also points out that the amount of water vapour in the upper atmosphere has increased in the past 50 years, perhaps as a result of increased methane in the atmosphere from farming and other human activities. Methane can react with oxygen in the atmosphere to create water molecules.

Noctilucent clouds can be seen from the ground with the naked eye, appearing after twilight when the sky first gets dark and also just before the sky brightens prior to sunrise. They glow a silvery blue colour. "They're very beautiful," Russell says. "You can't miss them – they're iridescent and bright and they have a lot of structure."

Seasonal effect

The northern hemisphere's noctilucent cloud season ends towards the end of August. When northern summer is over, the satellite will study the appearance of the clouds in the southern hemisphere, where they are prevalent between mid-November and mid-March.

The satellite's Cloud Imaging and Particle Size instrument produces panoramic images of the noctilucent cloud distribution. The Solar Occultation for Ice Experiment (SOFIE) provides measures the chemical makeup of the clouds and their altitude, and the Cosmic Dust Experiment measures space dust entering Earth's atmosphere.

Mission scientists are trying to determine whether this dust provides the "seeds" for ice particle formation for noctilucent clouds or if this role is instead played by dust particles blown upward from Earth.

Noctilucent clouds appear bluish-white in this view over the north pole from the AIM satellite. The black spot at centre is an area where no data was available

http://space.newscientist.com/article.ns?i...line-news_rss20

[magnetar]

How they originate would be interesting to know.

Edited June 30, 2007 by magnetar

[Picturesque Orion]

Hmm isn't that are where auroras appear? Could be because of aurora or not. Hmmm I am not so sure about this.... but the auroras mught iluminate the clouds.

[magnetar]

No, it has nothing to do with the aurorae. I don't know how they would ionize these clouds, or whatever you infer. Perhaps the sunlight makes them visible.

Edited July 2, 2007 by magnetar

[greggK]

No, it has nothing to do with the aurorae. I don't know how they would ionize these clouds, or whatever you infer. Perhaps the sunlight makes them visible.

I think it has to do with coronal ejections that turn the earth's magnetic field in on itself and that in turn reacts with the ions in the atmosphere to make it 'glow.' Yes, it is the sun that is causing that and that is why the ice is melting, not because of heat, but light.

[SameerPrehistorica]

very interesting,it looks great

[leadbelly]

These clouds float 80 kilometres above the ground and are made of tiny ice crystals. Because they are so high up, the Sun still reaches them and makes them glow after sunset and before sunrise, when the ground is in darkness.

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Some scientists suspect their proliferation is related to increasing greenhouse gases, which can actually cause the upper reaches of the atmosphere to cool.

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Temperatures where the clouds form hover at about -140° C.

<>

Methane can react with oxygen in the atmosphere to create water molecules.

<>

Noctilucent clouds can be seen from the ground with the naked eye, appearing after twilight when the sky first gets dark and also just before the sky brightens prior to sunrise. They glow a silvery blue colour.

The clouds are depicted generally as electric blue in color. They form as ice crystals with a size comparable to particles of cigarrette smoke, at temperatures around -140* C (-220* F), at around 83 km altitude.

The aurora is considered to have three main categories of chemical ionization and thermal levels. The more blue and violet levels of the aurora occur where general atmospheric temperatures are around 927* C (1700* F), at upwards of 1000 km. And, it involves not H2O, but molecular nitrogen.

Therefore, the illumination of noctilucent clouds is due to scattering of incoming visible electromagnetic-photons. Not, energized electrons or protons.

In order to penetrate down to the altitude of 80 km, it would probably require the heavier protons, since the electrons would not easily get there. Even so, at 80-85 km, the end result is a red glowing auroral display- not blue or electric blue. IMHO

[Ghost Ship]

Space Station Crew Photographs Mysterious Clouds that Shine at Night

They hover on the edge of space. Thin, wispy clouds, glowing electric blue. Some scientists think they're seeded by space dust. Others suspect they're a telltale sign of global warming.

They're called noctilucent or "night-shining" clouds (NLCs for short). And whatever causes them, they're lovely.

"Over the past few weeks we've been enjoying outstanding views of these clouds above the southern hemisphere," said space station astronaut Don Pettit during a NASA TV broadcast last month. "We routinely see them when we're flying over Australia and the tip of South America."

Skywatchers on Earth have seen them, too, glowing in the night sky after sunset, although the view from Earth-orbit is better. Pettit estimated the height of the noctilucent clouds he saw at 50 to 62 miles (80 to 100 km) ... "literally on the fringes of space."

"Noctilucent clouds are a relatively new phenomenon," says Gary Thomas, a professor at the University of Colorado who studies NLCs. "They were first seen in 1885" about two years after the powerful eruption of Krakatoa in Indonesia, which hurled plumes of ash as high as 80 kilometers into Earth's atmosphere.

Ash from the volcano caused such splendid sunsets that evening sky watching became a popular worldwide pastime. One sky watcher in particular, a German named T. W. Backhouse, noticed something odd. He stayed outside after the sun had set and, on some nights, saw wispy filaments glowing electric blue against the black sky. Noctilucent clouds. Scientists of the day figured the clouds were some curious manifestation of volcanic ash.

Eventually the ash settled and the vivid sunsets of Krakatoa faded. Yet the noctilucent clouds remained. "It's puzzling," says Thomas. "Noctilucent clouds have not only persisted, but also spread." A century ago the clouds were confined to latitudes above 50 degrees; you had to go to places like Scandinavia, Russia and Britain to see them. In recent years they have been sighted as far south as Utah and Colorado.

Astronaut Don Pettit is a long-time noctilucent cloud-watcher. As a staff scientist at the Los Alamos National Laboratory between 1984 and 1996, he studied noctilucent clouds seeded by high-flying sounding rockets. "Seeing these kinds of clouds [from space] ... is certainly a joy for us on the ISS," he said on NASA TV.

"Although NLCs look like they're in space," continues Thomas, "they're really inside Earth's atmosphere, in a layer called the mesosphere ranging from 50 to 85 kilometers high." The mesosphere is not only very cold (-193 Fahrenheit, or -125 Celsius), but also very dry--"one hundred million times dryer than air from the Sahara desert." Nevertheless, NLCs are made of water. The clouds consist of tiny ice crystals about the size of particles in cigarette smoke. Sunlight scattered by these crystals gives the clouds their characteristic blue color.

How ice crystals form in the arid mesosphere is the essential mystery of noctilucent clouds.

Ice crystals in clouds need two things to grow: water molecules and something for those molecules to stick to--dust, for example. Water gathering on dust to form droplets or ice crystals is a process called nucleation. It happens all the time in ordinary clouds.

Ordinary clouds, which are relatively close to Earth, get their dust from sources like desert wind storms. It's hard to waft wind-blown dust all the way up to the mesosphere, however. "Krakatoa may have seeded the mesosphere with dust in 1883, but that doesn't explain the clouds we see now," notes Thomas. "Perhaps," he speculates, "the source is space itself." Every day Earth sweeps up tons of meteoroids--tiny bits of debris from comets and asteroids. Most are just the right size to seed noctilucent clouds.

The source of water vapor is less controversial. "Upwelling winds in the summertime carry water vapor from the moist lower atmosphere toward the mesosphere," says Thomas. This is why NLCs appear during summer, not winter.

One reason for the recent spread of noctilucent clouds might be global warming. "Extreme cold is required to form ice in a dry environment like the mesosphere," says Thomas. Ironically, global warming helps. While greenhouse gases warm Earth's surface, they actually lower temperatures in the high atmosphere. Thomas notes that noctilucent clouds were first spotted during the Industrial Revolution--a time of rising greenhouse gas production.

Are NLCs a thermometer for climate change? A unusual sign of meteoroids? Or both? "So much about these clouds is speculative," says Thomas.

A NASA spacecraft scheduled for launch in 2006 should provide some answers. The Aeronomy of Ice in the Mesosphere satellite, or AIM for short, will orbit Earth at an altitude of 342 miles (550 kilometers). Although it's a small satellite, says Thomas, there are many sensors on board. AIM will take wide angle photos of NLCs, measure their temperatures and chemical abundances, monitor dusty aerosols, and count meteoroids raining down on Earth. "For the first time we'll be able to monitor all the crucial factors at once."

Meanwhile, all we can do is wait ... and watch. There's never been a better time to see noctilucent clouds. "During the summer months, look west perhaps 30 minutes to an hour after sunset when the Sun has dipped 6 to 16 degrees below the horizon," advises Thomas. If you see luminous blue-white tendrils spreading across the sky, you've probably spotted an NLC. Observing sites north of 40 degrees latitude are favored.

One more thing: don't forget your camera. According to astronaut Don Pettit, "you can never have too many pictures of noctilucent clouds."

source:Space.com