In much the same way that satellites allow forecasters to see the inner workings and development of a hurricane from its origins until the moment it reaches shore,
NASA’s STEREO spacecraft are now capturing images of solar storms and making real-time measurements of their magnetic fields from the moment they lift off the sun until the moment their pressure waves reach
Earth's shores.
Eruptions from the
sun’s outer atmosphere, or corona, can wreak havoc on earthly technology. These
solar hurricanes, known as coronal mass ejections (
CMEs), spew billions of tons of plasma into
space at thousands of miles per hour and carry some of the sun’s magnetic field with it.
These
solar storm clouds create a shock wave and a large, moving disturbance in the solar system. The
shock can accelerate some of the particles in space to high energies, a form of "solar cosmic rays" that can be hazardous to spacecraft and astronauts. The
CME material, which arrives days later, can disrupt
Earth’s magnetic field, or magnetosphere, and upper atmosphere.
Observations from
NASA’s twin Solar Terrestrial Relations Observatory (
STEREO)
spacecraft have allowed scientists to accurately measure for the first time the speed, trajectory, and three-dimensional
shape of
solar storms.
STEREO consists of two nearly identical observatories that make simultaneous observations of
CMEs from two different vantage points. One observatory 'leads'
Earth in its orbit around the sun, while the other observatory 'trails' the planet.
STEREO’s two vantage points provide a unique view of the anatomy of a solar storm as it evolves and travels toward Earth. Once the
CME arrives at the orbit of Earth, sensors on the satellites take in situ measurements of the solar storm cloud, providing a "ground truth" between what was seen at a distance and what is real inside the
CME.
The combination is providing
solar physicists with the most complete understanding to date of the inner workings of these storms. It also represents a big step toward predicting when and how the impact will be felt at Earth. The separation angle between the satellites affords researchers to track a
CME in three dimensions, something they have done several times in the past few years as they have learned to use this new space weather tool.
"We can now see a
CME from the time it leaves the solar surface until it reaches
Earth, and we can reconstruct the event in 3D directly from the images," said
Angelos Vourlidas, a
solar physicist at the Naval Research Laboratory, Washington, and project scientist for the Sun Earth Connection Coronal and Heliospheric Investigation aboard
STEREO.
"The in situ measurements from
STEREO and other near-Earth spacecraft link the physical properties of the escaping
CME to the remote images," said Antoinette "Toni" Galvin, a solar physicist at the University of New Hampshire, and the principal investigator on
STEREO’s Plasma and Suprathermal Ion Composition (
PLASTIC) instrument. "This helps us to understand how the internal structure of the
CME was formed and to better predict its impact on Earth."
Until now,
CMEs could be imaged near the sun but the next measurements had to wait until the
CME cloud arrived at Earth three to seven days later.
STEREO’s real-time images and measurements give scientists a slew of information—speed, direction, and velocity—of a
CME days sooner than with previous methods. As a result, more time is available for power companies and satellite operators to prepare for potentially damaging solar storms.
Much like a hurricane’s destructive force depends on its direction, size, and speed, the seriousness of a
CME’s effects depends on its size and speed, as well as whether it makes a direct or oblique hit across Earth’s orbit.
CMEs disturb the space dominated by
Earth's magnetic field. Disruptions to the magnetosphere can trigger the brightly colored, dancing lights known as auroras, or Northern and Southern Lights. While these displays are harmless, they indicate that
Earth’s upper
atmosphere and ionosphere are in turmoil.
Sun storms can interfere with communications between ground stations and satellites, airplane pilots, and astronauts. Radio noise from a storm can also disrupt cell phone service. Disturbances in the ionosphere caused by
CMEs can distort the accuracy of
Global Positioning System (
GPS) navigation and, in extreme cases, induce stray electrical currents in long cables and power transformers on the ground.
The twin
STEREO spacecraft were launched October 25, 2006, into
Earth’s orbit around the sun. The mission is the third in
NASA’s Solar Terrestrial Probes (
STP) program.
