We've finally had a solar storm! Ooooooh! Data! Plots! Explanations!
It started yesterday and continued today, as seen in the Space Weather Prediction Center's real-time Kp index. Kp is a single number that characterizes magnetospheric activity through ground based measurements of the Earth's magnetic field. It ranges from 0 to 9, 0 being nothing; 9 being doomsday. 4 or 5 is what I would call "stormy" or "disturbed" conditions. We hit that yesterday and reached a Kp of 7 early this morning.
It should be pointed out that while Kp was high, the "Disturbance Storm Time", or Dst index, was not very high (more accurately, it wasn't very low.) Dst is a rough measure of the amount of energy being deposited into the magnetosphere; the lower the number, the more energy there will be. This storm racked up a Dst of -40; a good storm will hit -100 or more.
I started receiving electron flux warnings from SWPC yesterday afternoon. This is a warning that the radiation belt electron flux (or how many electrons pass through a certain area per second) surpassed 1000 cm^-3*str^-1*s^-1. These are "killer electrons", or electrons with enough energy to penetrate the outer shielding of spacecraft and cause electric charge buildup on internal circuits. While the 1000 mark is one of SWPC's warning levels, the exact "danger zone" for electron flux depends on each satellite and is rarely well known.
FYI- based on the plot quality and fonts used, SWPC is clearly using IDL to generate their output. They should switch to a more modern language *coughpythoncough*.
**EDIT** It was pointed out, rightfully so, that only a short time ago I was a die hard IDL fan. As such, this comment is a bit hypocritical. Whoops.
Let's take a look at what could be driving this activity. The first key item to look at is Interplanetary Magnetic Field (IMF, or the Sun's magnetic field that is locked in the solar wind and carried to Earth). Specifically, the Z-component or "Bz". When IMF Bz is negative, the IMF can couple to the Earth's magnetic field to deliver energy to the magnetosphere system. The coupling method is called magnetic reconnection; I'll get to this later... eventually. The other things to notice are a jump in both solar wind density and Earthward velocity. Both increases cause the magnetospheric system to be driven harder, which we saw in the electron flux and in the Kp index. I'll need to see more data to figure out what kind of solar storm this is, but right now I'd guess that this is a high-speed-stream event.
I'll follow up on this storm and let you know if anything really fun happens with it.