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NCAR BREAKTHROUGHS FOCUS ON SOLAR HALOS, SUNSPOT CYCLES

A new instrument developed at the National Center for Atmospheric Research (NCAR) has captured landmark imagery of fast- evolving magnetic structures in the solar atmosphere. Steven Tomczyk (NCAR High Altitude Observatory) will present the images on Monday, May 31, at the annual meeting of the American Astronomical Society (AAS) in Denver.

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."

Breakthrough Research to Improve Forecasts of Sunspot Cycles

Using a new computer model of the Sun, scientists have begun work on a groundbreaking forecast of the next cycle of sunspots. Mausumi Dikpati of the National Center for Atmospheric Research (NCAR) announced new research leading to an improved forecast of cycle 24 at the annual meeting of the American Astronomical Society (AAS) in Denver. Predicting features of the solar cycle may help society anticipate sunspots and associated solar storms, which can disrupt communications and power systems and expose astronauts to high amounts of radiation.

The forecast draws on research by scientists at NCAR's High Altitude Observatory indicating that the evolution of sunspots is caused by a current of plasma, or electrified gas, that circulates between the Sun's equator and its poles over a number of years. The forecasters believe the next solar cycle will begin in 2007 to 2008 if the plasma circulation, which has slowed down during the present solar cycle, continues to decelerate. That would mean cycle 24 would begin about a half-year later than if the cycles followed the standard 11-year span.

"We will spend the next several months incorporating additional plasma flow data into our model to determine the rising pattern of cycle 24," explains Dikpati, a leader of the research team. "Our focus will be on when the cycle is likely to reach maximum and cause geomagnetic storms in Earth's atmosphere."

In addition to Dikpati, the team includes NCAR scientists Giuliana de Toma, Peter Gilman, and Oran White, as well as Nick Arge of the University of Colorado and the National Oceanic and Atmospheric Administration. The next sunspot cycle is referred to as cycle 24 because of a numbering system that dates back to the eighteenth century. Solar scientists have tracked these cycles for some time but have not been able to model them with sufficient accuracy to make long-term predictions.

The team's computer model, known as the Predictive Flux-transport Dynamo Model, successfully accounts for the 11-year duration of the solar cycle as well as such mysterious events as the reversal of the Sun's magnetic north and south poles that occurs toward the end of each solar cycle.

The research may represent a breakthrough in helping society better prepare for solar storms. It focuses on the meridional flow pattern of plasma, which circulates between the equator and the poles over a period of about 17 to 22 years and is believed to transport imprints of sunspots that occurred over the previous two sunspot cycles. By analyzing these past solar cycles, scientists hope eventually to forecast sunspot activity about two solar cycles, or 22 years, into the future.

The work also may have implications for understanding stars that have similar properties to the Sun. Observations have shown that the faster such G stars rotate, the more disturbances they experience. This may indicate that the plasma flow on such stars is speeded up, thereby transporting sunspots more quickly and creating more stellar storms. "In all G stars, a similar dynamo may be operating," Dikpati says.

The model incorporates the current of plasma, which acts as a sort of conveyor belt of sunspots. The sunspot process begins with tightly concentrated magnetic field lines in the solar convection zone (the outermost layer of the Sun's interior). They rise to the surface at low latitudes and form bipolar sunspots, which are regions of concentrated magnetic fields. When these sunspots decay, they imprint the moving plasma with a type of magnetic signature. As the plasma nears the poles, it sinks about 200,000 kilometers (124,000 miles) back to the convection zone and starts returning toward the equator at a speed of about one meter (three feet) per second or slower. The increasingly concentrated fields become stretched and twisted by the internal rotation of the Sun as they near the equator, gradually becoming less stable than the surrounding plasma. This eventually causes coiled-up magnetic field lines to rise up, tear through the Sun's surface, and create new sunspots.

Since the plasma flows toward the equator, the theory explains why sunspots appear mostly in the Sun's midlatitudes early in the solar cycle and then gradually become more common near the equator. Sunspots also become increasingly powerful with the progress of the solar cycle because the continuous shearing of the imprints of the magnetic fields by the denser plasma beneath the surface of the Sun increases the strength of the spot- producing magnetic fields.

The NCAR team has received funding from the National Science Foundation and a NASA Living with a Star grant for its research. The National Center for Atmospheric Research and UCAR Office of Programs are operated by UCAR under the sponsorship of the National Science Foundation and other agencies.