[Aavso-sid-list] 4d ionosphere

[David Saum]

http://science.nasa.gov/headlines/y2008/30apr_4dionosphere.htm?list153297




            4D Ionosphere
           04.30.2008




            April 30, 2008: Today, NASA-funded researchers released to the 
general public a new "4D" live model of Earth's ionosphere. Without leaving 
home, anyone can fly through the layer of ionized gas that encircles Earth 
at the edge of space itself. All that's required is a connection to the 
Internet.

            "This is an exciting development," says solar physicist Lika 
Guhathakurta of NASA headquarters in Washington, DC. "The ionosphere is 
important to pilots, ham radio operators, earth scientists and even 
soldiers. Using this new 4D tool, they can monitor and study the ionosphere 
as if they're actually inside it."

            The ionosphere is, in a sense, our planet's final frontier. It 
is the last wisp of Earth's atmosphere that astronauts leave behind when 
they enter space. The realm of the ionosphere stretches from 50 to 500 miles 
above Earth's surface where the atmosphere thins to near-vacuum and exposes 
itself to the fury of the sun. Solar ultraviolet radiation breaks apart 
molecules and atoms creating a globe-straddling haze of electrons and ions.


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            Ham radio operators know the ionosphere well. They can 
communicate over the horizon by bouncing their signals off of the 
ionosphere-or communicate not at all when a solar flare blasts the 
ionosphere with X-rays and triggers a radio blackout. The ionosphere also 
has a big impact on GPS reception. Before a GPS satellite signal reaches the 
ground, it must first pass through ionospheric gases that bend, reflect and 
attenuate radio waves. Solar and geomagnetic storms that unsettle the 
ionosphere can cause GPS position errors as large as 100 meters. Imagine a 
pilot flying on instruments descending toward a landing strip only to 
discover it is a football field to the right.

            "Understanding the ionosphere is clearly important. That's why 
NASA's Living with a Star (LWS) program funded this work," says 
Guhathakurta, LWS program scientist. Space Environment Technologies, Inc. of 
California received the LWS grant and they partnered with Space Environment 
Corp. of Utah and the US Air Force to develop the 4D ionosphere.

            "The best way to appreciate the 4D ionosphere is to try it," 
says W. Kent Tobiska, president of Space Environment Technologies and chief 
scientist of its Space Weather Division. He offers these instructions:

            "One, download and install Google Earth."

            "Two, visit our web site and click on the link 'Total Electron 
Content.'"

            Wait for the file to load and presto-you're flying through the 
ionosphere: screenshot.

            "Colors represent electron content," Tobiska explains. "Bright 
red is high density; that's where radio communications are restricted to few 
or no frequencies. Blue denotes low density; no problem there."

            Using the intuitive Google Earth interface, users can fly above, 
around and through these regions getting a true 3D view of the situation. 
Make that 4D. "The fourth dimension is time. This is a real-time system 
updated every 10 minutes," he says.

            The 4D model can be fun and even a little addictive, warns 
Tobiska, who likes to use it to pilot an imaginary plane over the Arctic. "A 
growing number of commercial business flights are crossing the Arctic 
Circle," he says. "It's the shortest distance between, say, Chicago and 
Beijing and many other major cities."

            The ionosphere is particularly important to these lucrative 
flights. While they are over the Arctic, planes lose contact with most 
geosynchronous satellites and must rely on "old-fashioned" radio 
communications-a link that could be severed during a radio blackout. Using 
the 4D model, a flight controller could examine the ionosphere from the 
flyer's point of view and use that information to anticipate problems that 
could cause a flight to be delayed or diverted.

            The proper name of the system is CAPS, short for Communication 
Alert and Prediction System. Earth-orbiting satellites feed the system 
up-to-the-minute information on solar activity; the measurements are then 
converted to electron densities by physics-based computer codes. It is 
important to note, says Tobiska, that CAPS reveals the ionosphere not only 
as it is now, but also as it is going to be the near future. "Forecasting is 
a key aspect of CAPS available to our customers from, e.g., the Dept. of 
Defense and the airline industry."


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