I was curious as to the effect that yesterday’s event will have on the space weather, so I asked my space weathergirl buddy, solar physicist Dr. Barbara J. Thompson at Goddard. She wrote:

There are three major effects from solar “events” – light from flares, magnetic field & mass from eruptions, and energetic particles (ions and electrons) that can be caused by both flares and eruptions (also called coronal mass ejections or CMEs). These three broad classes are monitored because of the effects they have – see the table at the bottom of this page.

The above image shows the alerts that resulted from the eruption/flare – taken from this page at NOAA’s web site.

In general, flares cause radio interference, CMEs cause geomagnetic storms, and energetic particles cause radiation hazards. However, it’s a complicated system and there are always exceptions to any generalization!

The three different types of phenomena have different ways that they reach Earth. There’s a great explanation here and they have the following diagram:

In the diagram above, the flare is occurring on the Sun at a location where it can be seen from Earth, and the light from the flare takes 8 minutes to reach Earth. The flare yesterday was an M-class flare, which is large but not as large as an X-flare (which is ten times larger), but it had enough strength to have some impact.

The CME (eruption of magnetic field & mass) takes 1-5 days to reach Earth’s orbit, depending on how fast it’s going (1 day is *extremely* unusual). In the figure, the CME isn’t heading towards Earth. However, the forecasts are difficult if the CME isn’t going straight towards Earth. It you look at the diagram above, the CME isn’t hitting Earth. However, what if the CME expanded just a couple of degrees wider than the forecast? The Earth could get a glancing blow from the CME – it could either be hit by the CME itself or by the compressed or shocked fields lines near the CME (shown at the large pink region). Glancing blows are really hard to forecast. Yesterday’s event was opposite of the diagram – the CME was to the right of the Earth instead of the left, but it still was far enough away that anything more than a glancing blow is unlikely. Yesterday’s forecast model is here.

So, the flare’s already finished, and the CME is unlikely to hit us. That leaves energetic particles, which can reach Earth in as little as half an hour after a flare, but can happen for days an eruption. The diagram shows the two sources of the energetic particles — flares and the shock from a CME (note: CMEs don’t always have shocks, it depends on their interaction with the solar wind). The energetic particles move (primarily) along magnetic field lines, and the solar wind makes a spiral shape. Where the Earth crosses the spiral determines whether particles will reach Earth. In the diagram, none of the field lines from the CME’s shock are connected to Earth, but the flare’s SEP might (the red line with the two blue lines around it show the estimated location of the solar wind magnetic field lines. Since yesterday’s CME happened to the right of Earth’s orbit (instead of to the left, as in the diagram), the solar wind field lines were very closely connected to Earth.

The alerts timeline shown above does indicate that there’s an elevated chance of energetic particles continuing through tomorrow.

So, bottom line, probably no biggie for us, though someone in transit to another planet might have to hit the storm shelter. There’s more info over at Space Weather, where they’re predicting a greater-than-25% chance of geomagnetic storms tomorrow.

[Update a little while later]

Barbara has a lot more here, including a cleaned-up version of this explanation (which was an email), though I don’t see much of anything wrong with it.