There are many strange and ordinary lights in the sky. There are the stars, moon, planets and the Aurora Borealis for example. High in the sky, 60 to 65 miles above Earth's surface, winds rush through a little understood region of Earth's atmosphere at speeds of 200 to 300 miles per hour. Lower than a typical satellite's orbit, higher than where most planes fly, this upper atmosphere jet stream makes a perfect target for a particular kind of scientific experiment: the sounding rocket. 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. When they go up, they will release materials that will be visible milky white clouds which will make the jet stream velocity and direction trackable. There will be a new light in the sky just off the US Atlantic coast.
There are many strange and ordinary lights in the sky. There are the stars, moon, planets and the Aurora Borealis for example. High in the sky, 60 to 65 miles above Earth's surface, winds rush through a little understood region of Earth's atmosphere at speeds of 200 to 300 miles per hour. Lower than a typical satellite's orbit, higher than where most planes fly, this upper atmosphere jet stream makes a perfect target for a particular kind of scientific experiment: the sounding rocket. 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. When they go up, they will release materials that will be visible milky white clouds which will make the jet stream velocity and direction trackable. There will be a new light in the sky just off the US Atlantic coast.
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Jet streams are fast flowing, narrow air currents found in the atmospheres of some planets, including Earth. The main jet streams are located near the tropopause, the transition between the troposphere (where temperature decreases with altitude) and the stratosphere. The major jet streams on Earth are westerly winds (flowing west to east). Their paths typically have a meandering shape; jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including the opposite direction of most of the jet.
The strongest jet streams are the Polar jets, at around 7–12 km (23,000–39,000 ft) above sea level, and the higher and somewhat weaker Subtropical jets at around 10–16 km (33,000–52,000 ft). The Northern Hemisphere and the Southern Hemisphere each have both a polar jet and a subtropical jet.
"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."
Determining what drives these winds requires precise understanding of the way the winds move and what kind of turbulence they show. To get an idea of the task at hand, imagine mapping not just the ups and downs of ocean waves but the attendant surf, undertow, and tides, all from 60 miles away and in only 20 minutes. To accomplish this, the five sounding rockets will launch from NASA's Wallops Flight Facility in Virginia releasing a chemical tracer into the air. The chemical – a substance called trimethyl aluminum (TMA) -- forms milky, white clouds that allow those on the ground to see the winds in space and track them with cameras. In addition, two of the rockets will have instrumented payloads to measure pressure and temperature in the atmosphere.
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.
Sounding rockets are usually launched one or two at a time, so launching five at once will call for specific timing and direction to gather the required data. The rockets must be launched on a clear night between March 14 and April 3. Scientists will then 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 work with this model.
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.
For further information and photo: http://www.nasa.gov/mission_pages/sunearth/missions/atrex-nightlight.html
