On October 19, 2003, a large solar flare erupted from the surface of the sun, drawing scientists' attention to three massive sunspot groups that, over the next two weeks, produced a total of 124 flares. Three of them were the biggest flares ever recorded. Along with these bursts of electromagnetic radiation came enormous clouds of plasma mixed with magnetic fields. Known as coronal mass ejections (CMEs), these unpredictable clouds consist of billions of tons of energetic protons and electrons. When directed earthward, CMEs can create problems. At last count, the fall's flares and CMEs affected more than 20 satellites and spacecraft (not including classified military instruments), prompted the Federal Aviation Administration to issue a first-ever alert of excessive radiation exposure for air travelers, and temporarily knocked out power grids in Sweden.
Historically, CMEs have struck the earth with little or vague warning. If they could be forecast accurately, like tomorrow's weather, then agencies would have time to prepare expensive instruments in orbit and on the ground for the correct size and moment of impact. Such precise predictions could soon emerge: last December researchers announced the early success of a forecasting instrument, called the Solar Mass Ejection Imager (SMEI), that can track CMEs through space and time.
Launched in January 2003 on a three-year test run, SMEI (affectionately known as "schmee") orbits the planet over the poles, along the earth's terminator, once every 101 minutes. On each orbit, three cameras capture images that, when pieced together, provide a view of the entire sky with the sun in the middle. The scattering plasma electrons of CMEs appear on SMEI images as bright clouds.
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Other sun-watching instruments can image CMEs, but they work like still cameras, taking single pictures of the sun. NASA's Solar and Heliospheric Observatory (SOHO), for example, can "see" CMEs erupting from the sun quickly but is soon blind to the path of the clouds. SOHO came in handy last fall when it caught two large CMEs headed for the earth, but it could not follow the ejecta nor provide an accurate impact time.
Instead of a SOHO-style snapshot camera, SMEI works more like a 24-hour surveillance system, constantly scanning and tracking. SMEI begins looking about 18 to 20 degrees from the sun and continues imaging beyond the earth. SMEI can determine the speed, path and size of a CME, allowing for refined and reliable impact forecasts. Such information is particularly useful, scientists say, in predicting small CME events. Such ejections can take anywhere from one to five days to reach our planet. Since its launch, SMEI has detected about 70 CMEs.
During last fall's solar storms, SMEI had its first big chance to prove worthy of its estimated $10-million price tag. Managed primarily by the Air Force Research Laboratory at Hanscom Air Force Base in Massachusetts, about 20 air force and university scientists have been developing SMEI over the past 20 years. At the December 2003 American Geophysical Union meeting in San Francisco, Janet Johnston, SMEI's program manager, proudly announced that SMEI had successfully detected two of the autumn's largest CMEs about 21 and 10 hours, respectively, before they struck the earth.
Unfortunately, scientists didn't know of the detection and tracking potential until after the storms hit the earth. Right now it takes about 24 hours for SMEI data to reach Hanscom because they travel through multiple ground-tracking stations. According to David F. Webb, a physicist at Boston College who is part of the SMEI team, precise forecasting demands a reduction in data-transmitting time from 24 to six hours. Such a reduction will require more researchers at ground-tracking stations to move information along and to inspect SMEI's output.
SMEI's data gathering may also need perfecting. Lead forecaster Christopher Balch of the Space Environment Center in Boulder, Colo., emphasizes that the CME signal must stand out better against other background light. Once improved, SMEI "could potentially fill a gap in our observations," Balch says, by allowing scientists to track CMEs precisely, thereby making "real-time" forecasts possible.
Krista West is based in Las Cruces, N.M.
