A new assessment of solar flares by a team led by CU-Boulder indicates some are more powerful and last longer than scientists had previously thought, findings that have implications for mitigating damage by solar storms to navigation and communication systems on Earth. Image: NASA/SDO/AIA
NASA’s Solar Dynamics Observatory (SDO), 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,” says
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,” says 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
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%. 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,” says Woods, the
principal author on a paper appearing in today’s online edition of
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 sec, 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,” says 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,” says 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, says Woods. “If GPS positions on Earth are off
by 100 ft or so because of disruption in the ionosphere, it wouldn’t be a big
deal for someone driving down a highway,” he says. “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
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 sec 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 hr a day, to help us forecast
what the sun is doing,” says Woods.
LASP has a long history of making solar measurements dating
back to the 1940s, even before NASA was formed, says 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,”
says Woods. “Our primary focus is getting science results, and our
students are helping with the data analysis for the EVE experiment.”