NASA - Carrington-class CME Narrowly Misses Earth

The close shave happened almost two years ago. On July 23, 2012, a plasma cloud or "CME" rocketed away from the Sun as fast as 3000 km/s, more than four times faster than a typical eruption. The storm tore through Earth orbit, but fortunately Earth wasn't there. Instead it hit the STEREO-A spacecraft. Researchers have been analyzing the data ever since, and they have concluded that the storm was one of the strongest in recorded history.

1st SEGMENT
While I did not have a direct view of the region which launched the large coronal mass ejection (CME) of July 23, 2012, it still managed to catch a glimpse of the solar plasma as it launched into space.

The eruption becomes visible at timestamp 02:14:24 UTC in the lower right side of the movies below.

2nd & 3r SEGMENT
STEREO-A, at a position along Earth's orbit where it has an unobstructed view of the far side of the Sun, could clearly observe possibly the most powerful coronal mass ejection (CME) of solar cyle 24 on July 23, 2012. The visualizations on this page cover the entire day.

We see the flare erupt in the lower right quadrant of the solar disk from a large active region. The material is launched into space in a direction towards STEREO-A. This creates the ring-like 'halo' CME visible in the STEREO-A coronagraph, COR-2 (blue circular image).

As the CME expands beyond the field of view of the COR-2 imager, the high energy particles reach STEREO-A, creating the snow-like noise in the image. The particles also strike the HI-2 imager (blue square) brightening the image.

4th SEGMENT
Like me, Little SDO, STEREO-B did not have a direct view of the coronal mass ejection (CME) launched by the Sun on July 23, 2012. However, the active region involved was very close to the limb of the sun (lower left quadrant) and STEREO-B provided an excellent view of plasma launched in both ultraviolet light and the white-light coronagraph

5th & 6th SEGMENT
In the last visualizations, generated from the Enlil space weather model, green represents particle density, usually protons and other ions. In green, we see the Parker spiral moving out from the Sun generated by the Sun's current sheet

Red represents particles at high temperatures and shows the CME is hotter than the usual solar wind flow. Large changes in density are represented in blue. These three colors sometimes combine to tell us more about the characteristics of the event (noted in the 3-color Venn diagram below).

Since this was a large and potentially disruptive event, the obvious question is why it didn't damage STEREO-A. The reason is that as this cloud of charged particles move through space, they alter magnetic fields which can induce electric voltages in electrical conductors. The intensity of these voltages are proportional to the size of the electrical conducting path. The STEREO-A spacecraft is small enough that the induced voltages are small and the spacecraft is designed to withstand them.

However, if this CME had struck Earth's magnetosphere, which has a much stronger magnetic field, the changing magnetic field would induce much larger voltages in systems with long electrical conductors, such as power lines that run over long distances. These significantly higher voltages can damage power transformers.

Credit: NASA Solar Dynamics Observatory (Little SDO), NASA STEREO, Dusan Odstrcil (GMU), Leila Mays (CUA) and Janet Luhmann (UCB) and NASA's Scientific Visualization Studio.