Our sun is a volatile star: explosions of light, energy and solar materials regularly dot its surface. Sometimes an eruption is so large it hurls magnetized material into space, sending out clouds that can pass by Earth's own magnetic fields, where the interactions can affect electronics on satellites, GPS communications or even utility grids on the ground.
The clouds can be large or small. They can be relatively slow or as fast as 3,000 miles per second, but only one component has a strong effect on how much a CME will arrange the magnetic fields in near-Earth space. If they are aligned in the same direction as Earth's -- that is, pointing from south to north -- the CME will slide by without much effect.
This image of the sun from Jan. 7, 2014, combines a picture of the sun captured by NASA's Solar Dynamics Observatory, or SDO, with a model of the magnetic field lines using data that is also from SDO. A new model based on such data may one day help space weather forecasters better predict how eruptions from the sun will behave at Earth.
If aligned in the opposite direction, however, Earth's magnetic fields can be completely rearranged. Indeed, it has happened that giant, fast moving CMEs have had little effect at Earth, while small ones have caused huge space weather storms, dependent on that one factor of where the magnetic fields point.
But right now we don't have much advance notice of how a CME's magnetic fields are arranged. We can only measure the fields as the CME passes over satellites close to Earth.
"What we have now is effectively only a 30 to 60 minute heads up of a CME's configuration before it hits Earth's magnetosphere," said Neel Savani, a space scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "We don't have a real time method for measuring or modeling this magnetic field more than an hour before a space weather impact."
Savani described a new model to measure the magnetic field configuration significantly further ahead of time in a paper appearing in Space Weather on June 9, 2015. The model is now undergoing testing, but if it's robust, then scientists might finally have a tool to predict a CME's magnetic configuration from afar. And that means forecasters could give utility grid and satellite operators a full 24-hour advance warning to protect their systems -- crucial time to protect their assets.
While we have no tools that can observe the magnetic configuration of a CME directly as it is traveling toward us, Savani made use of NASA's Solar Dynamics Observatory to observe the magnetic fields of the initial eruption on the sun.
In the past, using such data to predict which direction the CME's magnetic fields point has not been very successful. However, Savani realized that earlier attempts simplified the eruptions too much, assuming they came from a single active region -- the magnetically complex spots on the sun that often give rise to solar eruptions. Savani's new method is able to incorporate the complex reality of CMEs having foot points in more than one active region.
"Once you can successfully measure the initial structure of the CME, the next step is to have a good understanding of how it evolves as it travels," said Savani.
We have no tools to measure the magnetic fields once a CME has moved away from the sun, but scientists do have ways of watching how the clouds expand, twist and grow as they race into space. Both NASA's Solar Terrestrial Relations Observatory, or STEREO, and the joint ESA/NASA Solar and Heliospheric Observatory, or SOHO, provide these observations using coronagraphs, which can focus in on the CME's progress by blocking the bright light of the sun.
By watching how the CME moves and changes in these coronagraphs, Savani's model tracks how the initial eruption evolves over time. Ultimately, the model can describe how the CME will be configured as it approaches Earth, and even which parts of the CME will have magnetic fields pointed in which direction.
So far Savani has tested his modeling method on eight different CMEs to show that his model's predictions corresponded with what actually happened. He will test even more examples to make sure the model is truly robust. If perfected, such models can be used by the Space Weather Prediction Center at the US National Oceanic and Atmospheric Association to provide alerts and forecasts to industries that require space weather forecasts, such as the military, the airlines and utility companies. But it's NASA's responsibility - as the research arm of the nation's space weather effort - to make sure a model is reliable enough for regular operational use. So Savani is working with the Community Coordinated Modeling Center at NASA Goddard to test his model.
"We'll test the model against a variety of historical events," said Antti Pulkkinen, director of the Space Weather Research Center at NASA Goddard. "We'll also see how well it works on any events we witness over the next year. In the end we'll be able to provide concrete information about how reliable a prediction tool it is."
Savani will also work to improve the user interface of his model. The goal is to create an easy-to-use application with standardized input and reliable output. Time will tell if Savani's model can help with characterization of CMEs, but if it works, scientists will have an advanced new tool to protect our home planet from the effects of space weather.
For more information about the Solar Dynamics Observatory, visit: http://www.
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