[meteorite-list] Meteors and the Weather

[Pete Pete]

http://www.sandia.gov/news-center/news-releases/2005/physics-astron/lidar.html

Asteroid dust may influence weather, study finds
Nature paper: Burning asteroids may play ‘more important climate role than 
previously recognized’
The asteroid's dust trail as seen by lidar at Davis, Antarctica. The plot 
shows the strength of the vertical laser light scattered back from the 
atmosphere as a function of time and altitude above mean sea level. The dust 
trail, blown by the stratospheric winds, moved through the beam.
Download 300dpi JPEG image, “lidar-meteor-trail.jpg,” 156K (Media are 
welcome to download/publish this image with related news 
stories.)ALBUQUERQUE, N.M. — Dust from asteroids entering the atmosphere may 
influence Earth’s weather more than previously believed, researchers have 
found.

In a study to be published this week in the journal Nature, scientists from 
the Australian Antarctic Division, the University of Western Ontario, the 
Aerospace Corporation, and Sandia and Los Alamos national laboratories found 
evidence that dust from an asteroid burning up as it descended through 
Earth’s atmosphere formed a cloud of micron-sized particles significant 
enough to influence local weather in Antarctica.

Micron-sized particles are big enough to reflect sunlight, cause local 
cooling, and play a major role in cloud formation, the Nature brief 
observes. Longer research papers being prepared from the same data for other 
journals are expected to discuss possible negative effects on the planet’s 
ozone layer.

“Our observations suggest that [meteors exploding] in Earth’s atmosphere 
could play a more important role in climate than previously recognized,” the 
researchers write.

Scientists had formerly paid little attention to asteroid dust, assuming 
that the burnt matter disintegrated into nanometer-sized particles that did 
not affect Earth’s environment. Some researchers (and science fiction 
writers) were more interested in the damage that could be caused by the 
intact portion of a large asteroid striking Earth.

But the size of an asteroid entering Earth’s atmosphere is significantly 
reduced by the fireball caused by the friction of its passage. The mass 
turned to dust may be as much as 90 to 99 percent of the original asteroid. 
Where does this dust go?

The uniquely well-observed descent of a particular asteroid and its 
resultant dust cloud gave an unexpected answer.

On Sept. 3, 2004, the space-based infrared sensors of the U.S. Department of 
Defense detected an asteroid a little less than 10 meters across, at an 
altitude of 75 kilometers, descending off the coast of Antarctica. U.S. 
Department of Energy visible-light sensors built by Sandia National 
Laboratories, a National Nuclear Security Administration lab, also detected 
the intruder when it became a fireball at approximately 56 kilometers above 
Earth. Five infrasound stations, built to detect nuclear explosions anywhere 
in the world, registered acoustic waves from the speeding asteroid that were 
analyzed by LANL researcher Doug ReVelle. NASA’s multispectral polar 
orbiting sensor then picked up the debris cloud formed by the disintegrating 
space rock.

Some 7.5 hours after the initial observation, a cloud of anomalous material 
was detected in the upper stratosphere over Davis Station in Antarctica by 
ground-based lidar.

“We noticed something unusual in the data,” says Andrew Klekociuk, a 
research scientist at the Australian Antarctic division. “We’d never seen 
anything like this before — [a cloud that] sits vertically and things blow 
through it. It had a wispy nature, with thin layers separated by a few 
kilometers. Clouds are more consistent and last longer. This one blew 
through in about an hour.”

The cloud was too high for ordinary water-bearing clouds (32 kilometers 
instead of 20 km) and too warm to consist of known manmade pollutants (55 
degrees warmer than the highest expected frost point of human-released solid 
cloud constituents). It could have been dust from a solid rocket launch, but 
the asteroid’s descent and the progress of its resultant cloud had been too 
well observed and charted; the pedigree, so to speak, of the cloud was 
clear.

Computer simulations agreed with sensor data that the particles’ mass, 
shape, and behavior identified them as meteorite constituents roughly 10 to 
20 microns in size.

Says Dee Pack of Aerospace Corporation, “This asteroid deposited 1,000 
metric tons in the stratosphere in a few seconds, a sizable perturbation.” 
Every year, he says, 50 to 60 meter-sized asteroids hit Earth.

Peter Brown at the University of Western Ontario, who was initially 
contacted by Klekociuk, helped analyze data and did theoretical modeling. He 
points out that climate modelers might have to extrapolate from this one 
event to its larger implications. “[Asteroid dust could be modeled as] the 
equivalent of volcanic eruptions of dust, with atmospheric deposition from 
above rather than below.” The new information on micron-sized particles 
“have much greater implications for [extraterrestrial visitors] like 
Tunguska,” a reference to an asteroid or comet that exploded 8 km above the 
Stony Tunguska river in Siberia in 1908. About 2150 square kilometers were 
devastated, but little formal analysis was done on the atmospheric effect of 
the dust that must have been deposited in the atmosphere.

The Sandia sensors’ primary function is to observe nuclear explosions 
anywhere on Earth. Their evolution to include meteor fireball observations 
came when Sandia researcher Dick Spalding recognized that ground-based 
processing of data might be modified to record the relatively slower flashes 
due to asteroids and meteoroids. Sandia computer programmer Joe Chavez wrote 
the program that filtered out signal noise caused by variations in sunlight, 
satellite rotation, and changes in cloud cover to realize the additional 
capability. The Sandia data constituted a basis for the energy and mass 
estimate of the asteroid, says Spalding.

The capabilities of defense-related sensors to distinguish between the 
explosion of a nuclear bomb and the entry into the atmosphere of an asteroid 
that releases similar amounts of energy — in this case, about 13 kilotons — 
could provide an additional margin of world safety. Without that 
information, a country that experienced a high-energy asteroid burst that 
penetrated the atmosphere might provoke a military response by leaders who 
are under the false impression that a nuclear attack is underway, or lead 
other countries to assume a nuclear test has occurred.

More detailed papers are slated for the Journal of Geophysical Research and 
the Journal of Meteoritics and Planetary Science, Pack says.