 The coronal mass ejection, as photographed bySTEREO | |
| Coronal mass ejection | |
|---|---|
| First observed | July 23, 2012 (2012-07-23) |
Part ofsolar cycle 24 | |
Thesolar storm of 2012 was asolar storm involving an unusually large and strongcoronal mass ejection that occurred on July 23, 2012. It missedEarth by a margin of roughly nine days, as theSun's equatorrotates around its own axis once over a period of about 25 days.[1]
The region that produced the outburst was thus not pointed directly towards Earth at that time. The strength of the eruption has been predicted to be comparable to the 1859Carrington Event that caused damage to electrical equipment worldwide, which at that time consisted mostly oftelegraph systems.[2]
At 02:08 UT on 23 July 2012, a largecoronal mass ejection (CME) was launched from the Sun.[3] The eruption emanated fromsolar active region 11520 and coincided with what was at most anX2.5-class solar flare.[4] The CME expelled a pair of adjacentmagnetic clouds that drove a fast-movingshock wave outward from the Sun.[3] The eruption tore through Earth's orbit, hitting theSTEREO-A spacecraft.[2] The spacecraft is a solar observatory equipped to measure such activity, and because it was far away from the Earth and thus not exposed to the strong electrical currents that can be induced when a CME hits the Earth'smagnetosphere,[2] it survived the encounter and provided researchers with valuable data. Spacecraft observations recorded the shockwave at 20:55 UTC on 23 July while the magnetic clouds arrived two hours later. The leading shock wave associated with the CME was travelling radially at a speed of around 3,300 km/s (2,100 mi/s) relative to STEREO-A by the time it reached the spacecraft. The CME travelled from the Sun to Earth's orbit in about 20.78 hours, indicating an average speed of 2,000 km/s (1,200 mi/s).[3]
Based on the collected data, the eruption consisted of two separate ejections which were able to reach exceptionally high strength as theinterplanetary medium around the Sun had been cleared by a smaller CME four days earlier.[2] Interaction between the primary CME and the preceding CMEs as they traversed the interplanetary medium also led to amplification of the magnetic field of the ejecta that continued by the time the primary CME reached Earth's orbit.[5]
The event occurred at a time of highsunspot activity duringsolar cycle 24.
Had the CME hit the Earth, it is likely that it would have inflicted serious damage to electronic systems on a global scale.[2] The resultinggeomagnetic storm may have had astrength of −1,150 to −600 nT, comparable to the impact of theCarrington Event.[5] A 2013 study estimated that the economic cost to the United States would have been between US$600 billion and $2.6 trillion.[6] Ying D. Liu, professor at China's State Key Laboratory of Space Weather, estimated that the recovery time from such a disaster would have been about four to ten years.[7]
The record fastest CME associated with theAugust 1972 solar storm is thought to have occurred in a similar process of earlier CMEs clearing particles in the path to Earth. This storm arrived in 14.6 hours, an even shorter duration after the parent flare erupted than for the great solar storm of 1859.
