NASA Data And New Techniques Yield Detailed Views Of Solar Storms
The solar storms, called Coronal Mass Ejections (CMEs), are being observed from NASA's twin Solar Terrestrial Relations Observatory, or STEREO, spacecraft launched in 2006. The duo represents a key component within a fleet of NASA spacecraft that enhance the capability to predict solar storms.
Previous spacecraft imagery did not clearly show the structure of a solar disturbance as it traveled toward Earth. As a result, forecasters had to estimate when storms would arrive without knowing the details of how they evolve and grow. New processing techniques used on STEREO data allow scientists to see how solar eruptions develop into space storms at the Earth.
"The clarity these new images provide will improve the observational inputs into space weather models for better forecasting," said Lika Guhathakurta, STEREO program scientist at NASA Headquarters in Washington.
CMEs are billion-ton clouds of solar plasma launched by the same sun explosions that spark solar flares. When they sweep past Earth, they can cause auroras, radiation storms that can disrupt sensitive electronics on satellites, and in extreme cases, power outages. Better tracking of these clouds and the ability to predict their arrival is an important part of space weather forecasting.
Newly released images from cameras on the STEREO-A spacecraft reveal detailed features in a large Earth-directed CME in late 2008, connecting the original magnetized structure in the sun's corona to the intricate anatomy of the interplanetary storm as it hit the planet three days later. When the data were collected, the spacecraft was more than 65 million miles away from Earth.
The spacecraft's wide-angle cameras captured the images. They detect ordinary sunlight scattered by free-floating electrons in plasma clouds. When these clouds in CMEs leave the sun, they are bright and easy to see. However, visibility is quickly reduced, as the clouds expand into the void. The clouds are about one thousand times fainter than the Milky Way, which makes direct imaging of them difficult. That also has limited our understanding of the connection between solar storms and the coronal structures that cause them.
"Separating these faint signals from the star field behind them proved especially challenging, but it paid off," said Craig DeForest, scientist at the Southwest Research Institute in Boulder, Colo. and lead author of an Astrophysical Journal article released online yesterday. "We have been drawing pictures of structures like these for several decades. Now that we can see them so far from the sun, we find there is still a lot to learn."
These observations can pinpoint not only the arrival time of the CME, but also its mass. The brightness of the cloud enabled researchers to calculate the cloud's gas density throughout the structure, and compare it to direct measurements by other NASA spacecraft. When this technique is applied to future storms, forecasters will be able to say with confidence whether Earth is about to be hit by a small or large cloud, and where on the sun the material originated.
STEREO's two observatories orbit the sun, one ahead of Earth and one behind. They will continue to move apart over time. STEREO is the third mission in NASA's Solar Terrestrial Probes program. The program seeks to understand the fundamental physical processes of the space environment from the sun to Earth and other planets.
The STEREO spacecraft were built and are operated for NASA by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the mission, instruments and science center. The STEREO instruments were designed and built by scientific institutions in the U.S., UK, France, Germany, Belgium, Netherlands, and Switzerland.
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