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In The Spotlight


Tuning in to the sun: China launches construction of world-class heliograph

By Chong Wu

Just days before China launched its third manned spaceship, the Chinese Academy of Sciences (CAS) announced its latest plans for space conquest: construction of one of the world’s largest and most advanced imaging spectroscopy instrument. Starting in 2010, the Chinese spectral radioheliograph (CSRH) will “tune in” to the Sun to capture low-frequency radio bursts of a phenomenon known as coronal mass ejection.

A computer-generated picture of the antenna array for China’s spectral radioheliograph.

Coronal mass ejection is considered a mystery in solar physics. However, it drives space weather, largely through the release of highly-magnetic energy and particle acceleration and transport. This can have a huge impact on satellite communication, high-latitude flight and space voyage.

“No one so far can explain how and where the ejection originates and how it develops,” said Yan Yihua, chief scientist for the CSRH project.

An impediment, he explained, is that currently available imaging instruments can capture frequencies of only 4GHz or above, failing to provide a complete picture of the ejection, which usually happens in a much lower frequency range.

The CSRH, however, will be one of the few heliographs in the world that can receive that low-range frequency: 400 MHz to 15 GHz. “We will finally have a chance to observe more closely where most magnetic field lines are spliced to one another during the solar storms,” Yan said.

Chinese researchers adjusting equipment for viewing a solar eclipse.

Scientists will also be able to trace the birth of the ejection and better evaluate its impact on the space environment, according to Fang Cheng, one of China’s leading solar physicists.

“A particular question is how the ejection can accelerate to a speed of up to 2,000 kilometers a second. As long as we understand how, we can be able to make a better prediction about space weather,” said Fang, a professor at Nanjing University and a CAS academician.

But the CNY 50 million (US $7.3 million) scope, to be based in Inner Mongolia, is only one part of the country’s solar observation force, according to Fang.

Also under construction is a new infrared, one-meter-diameter solar tower in Kunming, set to be completed next year for the observation of the spectrum of the Sun.

Finally, China is planning to dispatch two satellites into outer space: an explorer unit carrying a number of coronal imaging devices, and another, carrying the largest solar telescope of its kind in the world.

The scope— one meter in diameter, with a resolution of 70 kilometers for observation of the solar surface from 150 million kilometers— is already on line to launch, according to Fang.

The explorer unit, which will be dedicated to studying coronal mass ejections and flares, will take another five years to prepare. China is collaborating with France to launch the unit, dubbed the Small Explorer for Solar Eruptions (SMESE). It will include not only a far infrared telescope, but also a Lyman α imager and coronagraph and a hard X and γ ray spectrometer.

China’s new instruments will add to the growing global force of solar observation.

In the United States, that force takes the form of the Frequency-Agile Solar Radiotelescope (FASR), now under construction.

Tim Bastian, principal investigator of the FASR team, said both the CSRH and FASR would “introduce new data types and new observational tools” for addressing critical problems in solar science.

A close up of loops in a magnetic active region of the sun, observed in 2006. This powerful active region has produced a series of intense flares, particle storms, and coronal mass ejections. (Image courtesy of NASA Goddard Space Flight Center)

“The availability of two similar instruments at different longitudes will increase the amount of solar observing from the ground and will therefore increase the opportunities to collaborate with space-based instruments such as STEREO (Solar Terrestrial Relations Observatory), TRACE (Transition Region and Coronal Explorer), and RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Explorer), which are currently flying; and the Solar Dynamics Observatory, which will be launched next year,” he said in a written interview.

He agreed with Yan and Fang that once the two instruments were successfully built, there would be possibilities for both sides to share data and collaborate in research. This is especially true, given that radioheliographs have a maximum working window of 12 hours—or whenever the sun is in sight.

Bastian also pointed out that it is important to have as much continuous solar observing as possible for the accuracy of space weather forecast. “If a third instrument could be place in Europe, full coverage would be achieved,” he said.


Wu Chong is a freelance journalist who has written for China Daily and SciDev.net. She is also an editor for Global Environmental Review, a Chinese electronic magazine about environmental news.

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