NASA's Solar Dynamics Observatory, which is carrying a suite of instruments including a $32 million University of Colorado Boulder package, has provided scientists with new information that energy from some solar flares is stronger and lasts longer than previously thought.
Using SDO's Extreme ultraviolet Variability Experiment, or EVE instrument designed and built at CU-Boulder, scientists have observed that radiation from solar flares sometimes continues for up to five hours beyond the initial minutes of the main phase of a solar flare occurrence. The new data also show that the total energy from this extended phase of the solar flare peak sometimes has more energy than that of the initial event.
Solar flares are intense bursts of radiation coming from the release of magnetic energy associated with sunspots. Flares are our solar system's largest explosive events and are seen as bright areas on the sun. Their energy can reach Earth's atmosphere and affect operations of Earth-orbiting communication and navigation satellites.
"If we can get these new results into space weather prediction models, we should be able to more reliably forecast solar events and their effects on our communication and navigation systems on Earth," said CU-Boulder Senior Research Associate Tom Woods of the Laboratory for Atmospheric and Space Physics, who led the development of EVE. "It will take some time and effort, but it is important."
"Previous observations considered a few seconds or minutes to be the normal part of the flare process," said Lika Guhathakurta, lead program scientist for NASA's Living With a Star Program. "This new data will increase our understanding of flare physics and the consequences in near-Earth space where many scientific and commercial satellites reside."
On Nov. 3, 2010, a solar flare was observed by SDO. If scientists had only measured the effects of the solar flare as it initially happened, the information would have resulted in underestimating the amount of energy shooting into Earth's atmosphere by 70 percent. The new capability with SDO observations will provide a much more accurate estimation of the total energy input into Earth's environment.
"For decades, our standard for flares has been to watch the X-rays as they happen and see when they peak," said Woods, the principal author on a paper appearing in online in the Astrophysical Journal. "That's our definition for when a flare goes off. But we were seeing peaks that didn't correspond to the X-rays."
Over the course of a year, the team used the EVE instrument to record graphs that map out each wavelength of light as it gets stronger, peaks and diminishes over time. EVE records data every 10 seconds, and thus EVE has observed numerous flares. Previous instruments only measured every hour and a half or didn't look at all the wavelengths simultaneously as SDO can.
"We are seeing something that is new and surprising about the physics of solar flares," said CU-Boulder doctoral student and paper co-author Rachel Hock. "When we looked at the observations from our instruments aboard SDO and compared them with our physical models, the results were consistent with each other," said Hoch of the astrophysical and planetary sciences department. "That was good news to us."
Because this previously unrealized extra source of energy from the flare is equally important in its impact on Earth's atmosphere, Woods and his colleagues are now studying how the late phase flares can influence space weather. In addition to impacting communication and navigation systems, strong solar flares can influence satellite drag and the decay of orbital debris.
When the ionosphere of Earth is disturbed by solar flares and coronal mass ejections, the communication between Earth-based instruments and GPS satellites can degrade, said Woods. "If GPS positions on Earth are off by 100 feet or so because of disruption in the ionosphere, it wouldn't be a big deal for someone driving down a highway," he said. "But if a farmer is using GPS to help determine precisely where to plant particular seeds, that GPS signal error could make a big difference."
To complement the EVE graphical data, scientists used images from another SDO instrument called the Advanced Imaging Assembly, or AIA, built by Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif. Analysis of the images showed the main phase flare eruption and the secondary phase as exhibited by coronal loops or magnetic field lines far above the original flare site. These extra loops were longer and became brighter later than the original set and these loops were also physically set apart from those earlier ones.
SDO was launched on Feb. 11, 2010, and is the most advanced spacecraft ever designed to study the sun and its dynamic behavior. The advanced spacecraft provides images with clarity 10 times better than high-definition television and provides more comprehensive science data faster than any solar observing spacecraft in history.
EVE includes three spectrographs -- two built at CU-Boulder's LASP -- to measure the solar extreme ultraviolet radiation. By making measurements every 10 seconds at 10 times the resolution of previous instruments, EVE is providing scientists and space weather forecasters with the information to provide more accurate, real-time warnings of communications and navigation outages. "We can look at data every minute, 24 hours a day, to help us forecast what the sun is doing," said Woods.
LASP has a long history of making solar measurements dating back to the 1940s, even before NASA was formed, said Woods. LASP projects have ranged from designing, building and flying NASA's Solar Mesospheric Explorer Satellite, which measured the sun's effect on ozone production and destruction of ozone in the 1980s, to the Solar Radiation and Climate Experiment, a $100 million NASA satellite designed, built and now being controlled by LASP to measure the effects of solar radiation on Earth's climate.
"We have a great tradition of working with students in all phases of our programs, starting with helping to design the instruments, helping to calibrate and test them as well as helping to operate them," said Woods. "Our primary focus is getting science results, and our students are helping with the data analysis for the EVE experiment."
NASA's Goddard Space Flight Center in Greenbelt, Md., built, operates and manages the SDO spacecraft for NASA's Science Mission Directorate in Washington, D.C. SDO is the first mission of NASA's Living with a Star Program, or LWS. The goal of LWS is to develop the scientific understanding necessary to address those aspects of the connected sun-Earth system that directly affect our lives and society.
- Thomas N. Woods, Rachel Hock, Frank Eparvier, Andrew R. Jones, Phillip C. Chamberlin, James A. Klimchuk, Leonid Didkovsky, Darrell Judge, John Mariska, Harry Warren, Carolus J. Schrijver, David F. Webb, Scott Bailey and W. Kent Tobiska. New Solar Extreme-ultraviolet Irradiance Observations during Flares. Astrophysical Journal, 2011; DOI: 10.1088/0004-637X/739/2/59
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