Shiny Ice Clouds Collecting at Earth's Edge

Feb. 26, 2003 -- Lately, astronauts on board the International Space Station have seen some scintillating views.

At the edge of space — the same cold region where space shuttle Columbia broke up into a trail of debris — shiny, silvery blue clouds have been hovering.

The high-altitude ice clouds are called noctilucent or "night-shining" clouds, and astronauts as well as Earth-bound scientists have been puzzled by their growing abundance.

The clouds are visible from space and from the ground over areas that are experiencing summer weather. Astronauts on the space station are seeing them over the southern hemisphere where it's now warm.

"We've seen definite changes," said John Olivero, a professor of physical science at Embry-Riddle Aeronautical University in Daytona Beach, Fla. "It appears the particles that make up the clouds have gotten slightly bigger with time and it appears the clouds are now visible further away from the poles than they have been before."

Volcanic Beginning

The last time these high, shiny clouds appeared in great numbers was after the 1883 eruption of the island volcano, Krakatoa, in Indonesia. The explosion hurled plumes of ash up to 50 miles into the air and caused spectacular sunsets.

The ash particles also served as rare anchors to water vapor at high altitudes and the vapor condensed to ice, forming the brilliant blue clouds. Sky gazers who stayed up late following the eruption reported seeing wispy, glowing streaks in the night sky. Before this incident there were no reported sightings of noctilucent clouds.

But why so many night shining clouds now?

"It's still being debated," says Chester Gardner, an atmospheric scientist at the University of Illinois at Urbana.

One reason scientists are having such a hard time understanding the shimmering clouds is their location. At 30-60 miles above Earth, the mesosphere is also known as the "ignorosphere" due to its inaccessibility. The region is too far to reach by weather balloon and yet it sits below where orbiting satellites or other craft might orbit because its heavier atmosphere would cause too much drag.

So far most data about the region has been gleaned from remote imaging by distant satellites or by rockets that zoom through the region only briefly and then fall back to Earth.

Greenhouse Gases Could Make Clouds

Still, researchers have learned enough to conclude that global warming is perhaps the most likely factor behind the increasing cloudiness at Earth's edge.

Computer models show that two greenhouse gases could have key effects on the mesosphere.

Carbon dioxide may absorb the sun's rays, making it warmer on Earth's surface, but it also radiates heat. Once it reaches the mesosphere, it's believed carbon dioxide radiates heat out into space and further cools the already frigid region. Extreme cold temperatures — around -225 degrees Fahrenheit — trigger water vapor to solidify into ice to form the clouds.

Water is also a critical ingredient in cloud formation and Gardner explains methane, another greenhouse gas, might be adding water to the high atmosphere. Methane is made up of one carbon atom and four hydrogen atoms. In the upper atmosphere ultraviolet rays break apart methane and the free hydrogen atoms combine with oxygen to form water. The water vapor then freezes to form the clouds.

Columbia's Trace at Edge of Space

Just after Columbia broke up in Earth's upper atmosphere, some questioned whether the little-understood clouds might have played a role in causing the accident. In fact, space station astronauts had recently remarked on the prevalence of the clouds over the southern hemisphere.

"Over the past few weeks we've been enjoying outstanding views of these clouds," astronaut Don Petit said during a NASA TV broadcast in January. "We routinely see them when we're flying over Australia and the tip of South America."

But Gardner and Olivero dismiss the idea that noctilucent clouds played a part in Columbia's demise since the clouds occur only during summer months when the upper atmosphere actually becomes colder and can cause water vapor to form ice. Columbia broke up over the current winter climate of the northern hemisphere.

But Columbia's demise could have altered the nature of the mesosphere — at least temporarily. Tiny particles from the break-up of the shuttle could have added to the amount of debris in the region — normally left behind only by passing meteorites.

"I'm sure there was some addition of material," said Olivera. "But my guess is by the time these clouds normally start forming in June, most of it will have moved out of the area."

While scientists aren't certain about the exact causes behind the increase in upper atmosphere clouds, research so far suggests they aren't altering Earth's climate. Instead they appear to be signaling a change that is already under way.

"Until the late 1880s, these clouds weren't seen at all," said Olivero. "Now they're bigger and more broadly dispersed. I'm convinced something is causing the changes."