Tuesday, March 13, 2012

A Jet Stream Study to Light Up the Sky

Update:  The mission was launched around 5 a.m. March 27.  Some photos are coming soon.

Little is known about the about the atmosphere above 50 miles, yet below where spacecraft orbit.  This is generally known as the Thermosphere above the Mesopause (See the graphic to the left, Image Credit: NASA).  The only way to study this region is with sounding rockets.  Some 35 to 40 feet long, sounding rockets shoot up into the sky for short journeys of eight to ten minutes, allowing scientists to probe difficult-to-reach layers of the atmosphere.

NASA will be conducting an experiment aimed at studying high-level winds near the edge of space at altitudes of 60 to 65 miles.  Winds at this altitude move at speeds of 200 to 300 miles per hour.  To study the winds NASA will release trimethyl aluminum which forms milky, white clouds that allow those on the ground to "see" the winds in space and track them with cameras.

Five sounding rockets will be launched in approximately five minutes to study these high-altitude winds and their intimate connection to the complicated electrical current patterns that surround Earth. First noticed in the 1960s, the winds in this jet stream shouldn't be confused with the lower jet stream located around 30,000 feet, through which passenger jets fly and which is reported in weather forecasts. This rocket experiment is designed to gain a better understanding of the high-altitude winds and help scientists better model the electromagnetic regions of space that can damage man-made satellites and disrupt communications systems. The experiment will also help explain how the effects of atmospheric disturbances in one part of the globe can be transported to other parts of the globe in a mere day or two.

The experiment is known as the Anomalous Transport Rocket Experiment (ATREX).  It is scheduled for 1:30 a.m. on March 15.  The backup dates are March 16 through April 3.  There will be a webcast of the mission beginning 2 1/2 hours prior to launch and can be viewed at: http://sites.wff.nasa.gov/webcast.


The rockets will be launched on a clear night within a period of minutes, so the trails can all be seen at the same time. The trimethyl aluminum will then be released in space out over the Atlantic Ocean at altitudes from 50 to 90 miles. The cloud tracers will last for up to 20 minutes and will be visible in the mid-Atlantic region, and along the east coast of the United States from parts of South Carolina to New Jersey.

"This area shows winds much larger than expected," says Miguel Larsen, a space scientist at Clemson University who is the principal investigator for these five rockets, known as the Anomalous Transport Rocket Experiment (ATREX). "We don't yet know what we're going to see, but there is definitely something unusual going on. ATREX will help us understand the big question about what is driving these fast winds."

NASA/Goddard Space Flight Center has produced the following video on the mission:

video

Scientists will use special camera equipment to track the five clouds and measure how quickly they move away from each other. They can then plug this information into equations that will describe what kind of turbulence exists in the winds.

One possible kind of turbulence is called three-dimensional turbulence, turbulence much like what one sees flowing down a river and swirling around rocks or in gusting winds on Earth. If this is seen, it would suggest the winds move with laws of motion similar to those governing small-scale waves in water. Such waves might be driven by heat in the atmosphere that varies in the course of a day. This would jibe with one of the original theories for how the winds are created, and indeed there are those who think of this region as a kind of atmospheric "surf zone" in the sky. Another view is that the winds at that height are too fast to jibe with this model. Moreover, man-made tracers, such as Space Shuttle exhaust, do not break up and dissipate as one might expect from such turbulence, but remain remarkably coherent.

On the other hand, if ATREX sees winds that exhibit what's called two-dimensional turbulence, this would support a model based on a more directed, jet stream flow.

"In 3-D turbulence, one sees complicated movement," says Larsen. "But there's a tendency for 2-D turbulence to behave almost in the opposite manner – the airflow coalesces into single streams, like a jet stream."

This kind of airflow would also be strongly enhanced by the combination of electrical currents in the region and the rate of the Earth's rotation. Together, this connection might result in the fast, coherent streams of air so far observed.