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The flares and accompanying CMEs burst out of an ‘active region’ on the Sun’s photosphere, which is the surface we see from Earth.

“Appearance of this active region producing strong flares and several CMEs was very interesting after months of very low solar activity,” says Juha-Pekka Luntama, responsible for space weather within ESA’s Space Situational Awareness office.

“Although these eruptions are very difficult to predict, and the active region that produced these events has now rotated around to the far side of the Sun, we are keeping watch on the situation, particularly when the active region rotates back into view.”

First big event

ESA/NASA Sun-watching SOHO spacecraft

The first eruption occurred on 6 September, and produced a severe geomagnetic storm when it reached Earth on the evening of 7 September. Its arrival was detected by a number of ESA and NASA spacecraft watching our Sun or orbiting Earth.

The arrival also gave rise to increased auroras on 7 and 8 September, visible as far south as northern Germany in Europe and the northern USA in North America.

The flare and CME were accompanied by a flood of energetic atomic particles from the Sun. These could be detected by satellites in orbit, but not at ground level owing to the shielding effect of our atmosphere.

Second big event

The second eruption occurred on 10 September (see video above). This was associated with a large solar flare that also emitted a strong pulse of X-rays and a flood of extremely high-speed protons, some travelling near to the speed of light.

This CME was faster than the first one, but it, too, travelled off the direct Sun–Earth path and only a tail end of it washed across our planet on 12 September.

This event caused a strong increase in energetic particles, with increased levels of radiation detected at Earth’s surface by monitoring networks, and a moderate geomagnetic storm was observed on 12 and 13 September.