Mysterious glowing clouds targeted by NASA
17:07 26 May 2006
NewScientist.com news service
Maggie McKee
Glowing, silvery blue clouds that have been spreading around the world
and brightening mysteriously in recent years will soon be studied in
unprecedented detail by a NASA spacecraft.
The Aeronomy of Ice in the Mesosphere (AIM) mission will be the first
satellite dedicated to studying this enigmatic phenomenon. Due to
launch in late 2006, it should reveal whether the clouds are caused by
global warming, as many scientists believe.
"Noctilucent" clouds, which glow at night, form in the upper
atmosphere, at an altitude of about 80 kilometres, and their glow can
be seen just after sunset or just before sunrise.
"Even though the Sun's gone down and you're in darkness, the clouds
are so high up, the Sun is still illuminating them," explains AIM
principal investigator James Russell at Hampton University in
Virginia, US. Russell described the mission on Thursday at a meeting
of the American Geophysical Union in Baltimore, Maryland, US.
Bigger and brighter
The clouds were first observed above polar regions in 1885 –
suggesting they may have been caused by the eruption of Krakatoa two
years before. But they have spread to latitudes as low as 40° in
recent years. "They're also getting brighter, and each year there are
more of them than in the previous year," Russell told New Scientist.
Many researchers believe this proliferation is down to human
activities. "You need three things for clouds to form: particles that
water can condense onto; water; and cold temperatures," says Russell.
He says pollution and global warming are thought to be responsible for
two of those factors.
Atmospheric water may be boosted by livestock farming and the burning
of fossil fuels, which spew methane into the atmosphere: sunlight
breaks down the methane, releasing hydrogen that can bond with oxygen
to form water.
And greenhouse gases such as carbon dioxide actually help to cool the
upper atmosphere, where the clouds form. That is because the
atmospheric density is so low at that altitude that the gases cannot
trap heat as they do closer to the Earth's surface, and the heat is
simply radiated into space.
Alien ice
As yet, it is not clear what the source of the particles that "seed"
the clouds is. The clouds form during the local summer months, when
the pole is bathed in perpetual sunlight. So one possibility is that
warm air rising above the pole could carry dust upwards from lower
atmospheric altitudes, onto which water can condense.
But the dust could also have a cosmic source, dropping into the
atmosphere from space. "It may be there's a constant supply of
particles but a changing temperature and water environment makes the
conditions right to grow ice particles," says Russell.
AIM will use three instruments to study the clouds. One is a suite of
four cameras that will provide panoramic views of the poles and
clouds. Another, called the Solar Occultation for Ice Experiment
(SOFIE), will study the chemistry of the ice particles and clouds –
measuring molecules such as methane. It will also observe the Sun
through the atmosphere to measure how much sunlight is dimmed by dust
in the atmosphere.
The third instrument, called the Cosmic Dust Experiment, is a plastic
film that sits on top of the spacecraft. It will record every "hit"
from a dust particle that rains down on it from space.
Cloud umbrella
"We want to know why the clouds form and why they vary," says Russell.
"If there is a human connection, it'll tell us that we're doing
something to the atmosphere and that we need to determine what the
long-term consequences are."
Some scientists speculate that the clouds might actually help mitigate
global warming, says Russell. "If these clouds were to continue to
grow and cover broad areas of Earth, they would form something like a
thin, semi-transparent umbrella," he told New Scientist. "They would
reduce the amount of solar rays making it to the ground, so they could
actually reduce the effects of global warming."
The AIM satellite will launch into a polar orbit from California's
Vandenburg Air Force Base. Russell says it may lift off in December,
but its exact launch date has not been set because mission planners
are still working to minimise vibration forces on the spacecraft due
to its Pegasus XL launch rocket.
--
"Science is the record of dead religions." -- Oscar Wilde
"There are no absolute certainties in this universe. A man must try to
whip order into a yelping pack of probabilities, and uniform success is
impossible." -- Jack Vance
"Civilization is the interval between Ice Ages." -- Will Durant.
"War is God's way of teaching Americans geography" -- Ambrose Bierce
"Progress is the increasing control of the environment by life.
--Will Durant
Joseph R. Darancette
daranc@NOSPAMverizon.net
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