UT Dallas Project Helps Fill Out Picture of Earth’s Ionosphere
Researchers’ Instruments Reveal Surprises About Size and Shape of Electrically Charged Layer
Dec. 16, 2008
A space weather satellite with Coupled Ion-Neutral Dynamics Investigation (CINDI) instruments aboard have for the first time revealed the size and shape of the gaseous envelope of electrically charged particles that surrounds the globe.
Called the ionosphere, this essential border between Earth and space has now been mapped at its upper boundary and shown to occupy less height than expected.
|Measurements from CINDI instrumentation have made the first map of the ionosphere’s upper surface. It expands and contracts from day to night but has much less height than expected.|
A collaboration among NASA, the U.S. Air Force Research Laboratory (AFRL) and the University of Texas at Dallas, CINDI is revealing what happens during periods of low sunspot activity, when the upper atmosphere cools off.
The ionosphere plays a particularly important role in satellite communication and any type of technology that uses space-based communications. GPS systems used by ships, trucking companies, and airplanes depend on reliable, uninterrupted streams of information from satellites, which must punch a signal cleanly through the ionosphere.
“Any radio or location system signal that utilizes space-based communication has to go through the ionosphere,” said CINDI Principal Investigator Rod Heelis, director of the Hanson Center for Space Sciences at UT Dallas. “On its best day, the ionosphere just bends that signal rather like water bends light. On its worst day it can completely distort that signal so that it doesn’t make it out the other side.”
Predicting when these disturbances might occur is a key goal of the CINDI project and its satellite, the Communication/Navigation Outage Forecast System (C/NOFS).
CINDI reveals for the first time:
- A view of the ionosphere never seen before, during solar “quiet” times.
- A map showing the size and shape of the Earth’s ionosphere.
- That the ionosphere is up to 100 degrees cooler than previously thought.
- That the effective thickness of the ionospheric shell is less than expected.
- A link between the extent of the ionosphere and solar activity levels observed at solar minimum.
- A view of the daily expansion and contraction of the ionosphere around the equator.
“The ionosphere is extremely cold at night, leading to a much thinner altitude and less dense layer than we expected,” Heelis said. “We have found that it is up to 100 degrees cooler than we expected and the effective thickness of the ionospheric shell is smaller than we expected.”
Heelis said CINDI revealed that the ionosphere expands during the day, when the upper surface rises, but not as high as the team thought it might. Further, the daily expansion and contraction of the ionosphere has been observed continuously around the equator for the first time. Had sunspot activity not dropped off—with associated cooling of the ionosphere—scientists would not have been able to watch the ionosphere expand and contract.
The so-called “quiet time” view of the ionosphere, when sunspot activity is low, allows Heelis and Greg Earle, another UT Dallas physics professor and CINIDI team member, to study the region of the ionosphere that is hazardous to radio communications.
Heelis and Earle built the two instruments that comprise CINDI:
- The Ion Velocity Meter, which measures the direction and speed of ions as well as their density, temperature and chemical composition.
- The Neutral Wind Meter, which measures the speed and direction of the neutral atoms and molecules in the near vacuum of space.
The 20-pound package of sensors and electronic equipment was fabricated in Heelis’ UT Dallas laboratory with Earle’s assistance and in collaboration with Paul Mahaffey of NASA’s Goddard Space Flight Center.
CINDI was carried on the C/NOFS satellite that was launched on April 16, 2008 on a Pegasus XL rocket aboard Orbital Science Corporation’s L-1011 “Stargazer” jet. The C/NOFS mission was launched to explore ways to forecast disturbances in the Earth’s ionosphere that can result in a disruption of navigation and communication signals.
“Years ago, my basic question began as, ‘How does our space environment interact with the sun?’” Heelis said. “I was intellectually curious about that. But now, as we become more dependent on assets in space, answering that question has real importance to everyday commerce, to military and commercial communications and navigation. NASA and the Air Force want to know the answers, and it’s enlightening to see major agencies working with us at UT Dallas to share resources and work on these problems together.”