The largest solar flare in several years has disrupted some communications, though it was not in the right position to create auroral displays visible from lower latitudes.

The flare, which erupted on Feb. 15, sent what is called a coronal mass ejection, or CME, towards the Earth. A CME is billions of tons of charged particles, mostly protons.

When the charged particles come close to the Earth, they are forced to move along the magnetic field lines, creating the auroral displays and radio interference. In a worst case, they can damage electrical systems.

This CME hit the Earth's magnetic field under just the right conditions - or wrong ones, depending on your perspective - that a major magnetic storm did not erupt. Daniel Baker, director of the laboratory of atmospheric and space physics at the University of Colorado, said each CME carries its own magnetic field. If the field is aligned so that the CME's north magnetic pole is oriented towards the Earth's south magnetic pole, then much more energy is transferred and you get the bigger disturbances. If the reverse is true, as it was in this case, then the activity is more muted.

The disruptions that did occur happened mostly in China, he said, because China was on the day side of the Earth when the CME hit. Baker said the reported problems were with high-frequency radio communications.

Flares are classified according to how powerful they are, as A, B, C, M or X, with X being the most powerful. The Feb. 15 event was a class X.

Baker, also a professor in the astrophysical and planetary sciences department, said while solar flares and magnetic storms can damage electrical systems and satellites, they are important to study because they show how the system behaves when it is hit by high-energy phenomena. When you get extreme disturbances you get to see how the system behaves under extreme duress, he said. The relative rarity of CMEs that hit the Earth makes them exciting, as each one is different. As a colleague of mine said, if you've seen one storm you've seen one storm.

According to the National Oceanic and Atmospheric Administration, several more coronal mass ejections may reach Earth's atmosphere in the next two days.

The last major event was in 2003, on Halloween, when radio communications were disrupted over a much wider area. The most violent solar event ever recorded was in 1859, and it is known as the Carrington Event. It is named for the British astronomer, Richard Carrington, who observed the largest flare of the event, which erupted at the end of August.

The CME that emerged from the flare took only 18 hours to reach the Earth. Most CMEs take three to five days. The magnetic storm was so intense that auroras were observed as far south as Baltimore, and telegraph systems were damaged.

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