jueves, 4 de junio de 2009
Huge Waves Detected in Atmosphere
Researchers have detected giant, fast-moving waves of air, caused by thunderstorms and other disturbances, above Poker Flat, Alaska, where a new radar is churning out the first three-dimensional images of upper atmospheric phenomena in the polar region.
"People have been envisioning doing this project for 40 years," said Eric Donovan, an associate professor of physics and astronomy at the University of Calgary in Alberta, Canada. "There's just a lot going on in this region that we don't understand."
The radar combines 4,096 small antennas, each with its own transmitter, on a single instrument, rather than one giant dish equipped with one powerful transmitter. Rather than physically rotating the radar to point in different directions, the steering is done electronically by slightly phasing each of the antenna elements differently.
The radar, which can be run remotely via the Internet, can be very quickly adjusted to pinpoint and track velocity, temperature and other changes in the upper atmosphere.All the previous systems would take half an hour to make measurements of a region that we're interested in," Donovan told Discovery News. "That'd be like keeping a camera's exposure open for 30 minutes when you're trying to take a picture of the finish of a race. All you'd see are streaks."
"It has the ability to essentially take three-dimensional pictures of the ionosphere whereas traditional systems can only look in one direction because of steering limitations," added Michael Nicolls, a research scientist with SRI International in Menlo Park, Calif.
"This allows us, for example, to see wiggles in the ionosphere, and say 'Yes, these are atmospheric waves' and, in addition, figure out where they are coming from, which is very unique," Nicolls wrote in an email to Discovery News.
With the new capabilities, scientists hope to be able to trace atmospheric waves to their source, such as a thunderstorm or air slamming into a mountain.
"By building up this 3-D view showing the waves, we can see where the sources are," said Craig Heinselman, the principal investigator of the Advanced Modular Incoherent Scatter Radar, or AMISR. "It's the first time we've been able to look, especially at high latitudes, in multiple directions simultaneously."
Scientists have identified a few types of waves, some of which rip through the region of the atmosphere known as the mesopause, about 60 to 90 kilometers above the planet, and others in the thermosphere, roughly 200 to 300 kilometers in altitude.
The waves can be hundreds of kilometers long and travel at half the speed of sound.
"They are really enormous," Heinselman said.
Scientists will soon be expanding their view with a second AMISR system at Resolute Bay in Nunavut, Canada, which is within the polar cap.
"It is really uncharted territory," said Nicolls. "Who knows what we will find."
Nicolls and other scientists presented results from AMISR Poker Flat research at the American Geophysical Union conference in Toronto last week.