Image Caption: Twelve spacecraft in Earths magnetosphere in addition to other missions -- helped scientists better observe and understand an unusual January 2005 solar storm. The four Cluster spacecraft were in the solar wind, directly upstream of Earth. Picture not to scale. Credit: ESA

Karen C. Fox, NASAs Goddard Space Flight Center

A space weather storm from the sun engulfed our planet on Jan. 21, 2005. The event got its start on Jan. 20, when a cloud of solar material, a coronal mass ejection or CME, burst off the sun and headed toward Earth. When it arrived at our planet, the ring current and radiation belts surrounding Earth swelled with extra particles, while the aurora persisted for six hours. Both of these are usually signs of a very large storm indeed, this was one of the largest outpouring of solar protons ever monitored from the sun. But the storm barely affected the magnetic fields around Earth disturbances in these fields can affect power grids on the ground, a potential space weather effect keenly watched for by a society so dependent on electricity.

Janet Kozyra, a space scientist at the University of Michigan in Ann Arbor, thought this intriguing combination of a simultaneously weak and strong solar storm deserved further scrutiny. In an effort to better understand and some day forecast such storms and their potential effects on human technology, an unusual event like this can help researchers understand just what aspects of a CME lead to what effects near Earth.

There were features appearing that we generally only see during extreme space weather events, when by other measures the storm was moderate, said Kozyra. We wanted to look at it holistically, much like terrestrial weather researchers do with extreme weather. We took every single piece of data that we could find on the solar storm and put it together to see what was going on.

With observations collected from ground-based networks and 20 different satellites, Kozyra and a group of colleagues, each an expert in different aspects of the data or models, found that the CME contained a rare piece of dense solar filament material. This filament coupled with an unusually fast speed led to the large amount of solar material observed. A fortuitous magnetic geometry, however, softened the blow, leading to reduced magnetic effects. These results were published in the Aug. 14, 2014, issue of Journal of Geophysical Research, Space Physics.

The researchers gathered data from spacecraft orbiting in Earths ionosphere, which extends up to 600 miles above the planets surface, and satellites above that, orbiting through the heart of Earths magnetic environment, the magnetosphere. The massive amount of data was then incorporated into a variety of models developed at the University of Michigans Center for Space Environment Modeling, which are housed at the Community Coordinated Modeling Center at NASAs Goddard Space Flight Center in Greenbelt, Maryland, a facility dedicated to providing comprehensive access to space weather models.

With the models in hand, the team could put together the story of this particular solar storm. It began with the CME on Jan. 20, 2005. The European Space Agency and NASAs Solar and Heliospheric Observatory, or SOHO, captured images of the CME. At their simplest, CMEs look like a magnetic bubble with material around the outside. In this case, there was an additional line of colder, denser solar material an electrically charged gas called plasma inside called a solar filament. Solar filaments are ribbons of dense plasma supported in the suns outer atmosphere the corona by strong magnetic fields. Filament material is 100 times denser and 100 times cooler than the surrounding atmosphere. When the supporting magnetic fields erupt, the filaments are caught up in the explosive release that forms the CME. Despite observations that the majority of eruptions like this involve solar filaments, the filaments are rarely identified in disturbances that reach Earth. Why this might be, is a mystery but it means that the presence of the solar filament in this particular event is a rare sighting.

Subsequent observations of the CME showed it to be particularly fast, with a velocity that peaked at around 1800 miles per second before slowing to 600 miles per second as it approached Earth. Just how many CMEs have filaments or how the geometry of such filaments change as they move toward Earth is not precisely known. In this case, however, it seems that the dense filament sped forward, past the leading edge of the CME, so as it slammed into the magnetosphere, it delivered an extra big dose of energetic particles into near-Earth space.

What happened next was observed by a flotilla of Earth-orbiting scientific satellites, including NASAs IMAGE, FAST and TIMED missions, the joint European Space Agency, or ESA, and NASAs Cluster, the NASA and ESAs Geotail, the Chinese and ESAs Double Star-1; other spacecraft 1 million miles closer to the sun including SOHO and NASAs Advanced Composition Explorer, Wind various other spacecraft; as well as the National Science Foundation-supported ground-based SuperDARN radar network. At the time Cluster was in the solar wind directly upstream of Earth. Meanwhile, Double Star-1 was passing from the outer region of the planets magnetic field and entering the magnetosphere. This enabled it to observe the entry of the solar filament material as it crossed into near-Earth space.

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Researchers Use NASA And Other Data To Look Into The Heart Of A Solar Storm