NCAR Instrument Gets Breakthrough View Of Sun's Magnetic Halo

Animations from the coronal multichannel polarimeter, or CoMP, reveal turbulent, high-velocity magnetic features spewing outward from the Sun's surface. A sample animation can be viewed at the Web site below. The National Science Foundation, NCAR's primary sponsor, is providing funding for the instrument.

CoMP is expected to provide the best data to date on magnetic structures in the solar corona, the extremely hot halo around the Sun that becomes visible during eclipses. "People have measured coronal magnetism before," says Tomczyk, "but we believe this is the first time it's being done in a time sequence like this, where you can see an evolving structure. I think we're making important steps and demonstrating that this technology works.

Data from CoMP will help solar physicists relate magnetism in the corona to features emerging from the Sun, such as prominences and coronal mass ejections. Such features are the sources of "space weather," the solar storms that can disable electric grids and satellites and interfere with radio communications.

"CoMP will deliver measurable benefits to the nation and the global space physics community," says Paul Bellaire, program director for NSF's solar terrestrial research. "Space weather forecasters around the world provide tailored information to managers and policy makers responsible for the high tech infrastructure supporting our orbiting and Earth-based telecommunications, navigation, and power grid systems. CoMP's solar corona imaging capability will be a valuable tool for these forecasters, as well as for researchers of the near-Earth space environment, since the Sun is the driving force behind all space weather." The CoMP data being presented at the AAS meeting were collected during tests in January and March at the National Solar Observatory in Sunspot, New Mexico. Further tests are being conducted this month.

CoMP uses a telescope with a lens roughly eight inches wide to gather and analyze light from the corona, which is much dimmer than the Sun itself. It tracks magnetic activity around the entire edge of the Sun, covering much more area than previous instruments. It also collects data far more often than its predecessors--as frequently as a measurement every 15 seconds.

Closer to the Sun's surface, magnetism has been traced for over a decade by ground- and space-based instruments. These devices infer the magnetic field by measuring several components of visible radiation. Until recently, though, there was little hope of using this technique to analyze magnetism in the Sun's corona. Although the corona's temperatures are scorching (as high as 1.8 million degrees Fahrenheit, or 1.0 million degrees Celsius), the corona itself is far too thin to yield a strong signal. However, a new generation of super-sensitive, low-noise infrared sensors made CoMP possible.

The NCAR team also devised a way to take images in two wavelengths of light at the same time. This allows scientists to filter out light scattered by Earth's atmosphere into the telescope's field of vision while preserving the faint signal from the corona. CoMP's developers hope to pair the instrument with a larger telescope. "Ultimately you want to gather more light," says Tomczyk. "This would give us more detail and allow us to gather data faster, so that both the temporal and spatial resolution could be improved."