After a series of rather small and, quite frankly, boring space weather events over the past month, it looks like we have something interesting going on! We are in the middle of a decently-sized space weather storm, and NOAA’s Space Weather Prediction Center (SWPC) warns that it could get stronger tomorrow- reaching a “G3” level on their scale that ranges from G1 to G5.
A large solar event called a coronal mass ejection, or simply a CME, reached the ACE spacecraft around 21:00 UTC (or around 5pm EDT) on October 12. (ACE is situated just upstream of the Earth and is first chance for us to directly measure the solar wind before it hits Earth.) You can see the observations from ACE yourself at SWPC’s website. Typically, we look for strong, sudden jumps in solar wind speed and magnetic field intensity to find the arrival of a CME. However, the ACE real-time data is quite spotty right now, so full identification is difficult. The jump in these values is not very strong, but it’s there.
When we want to tell if a transient event, like a CME, will be geoeffective (that is, will cause a space weather storm at Earth), we want to look at the Interplanetary Magnetic Field (IMF). The most important factor is the direction of the solar wind: when it’s southward, energy transfer from the solar wind to the Earth is the most efficient. In ACE observations, this is seen in the Z-component of the IMF. When IMF BZ is negative, we should expect a strong storm. IMF BZ has been strongly southward for the past 12 hours, which is surprising! I would expect this to be a pretty strong storm.
When a storm is underway, there are several geomagnetic indices that tell us about the current conditions. These are values obtained from ground-based observations of perturbations in the Earth’s magnetic field, then processed into single numbers to help summarize what’s happening. Let’s look at these:
- First, there’s KP, which indicates activity on a scale from 1-9. NOAA considers anything 5 or above to be a storm, and we’re currently sitting at 6. Things get really exciting at 8 or 9, but 6 is not a storm to scoff at!
- Next, there’s DST, (bottom plot, in red) which stands for Disturbance Storm Time. DST attempts to indicate the amount of energy stored in the inner magnetosphere region, measured in nano-Tesla or nT. A value of zero is observed during quiet times; a more negative number indicates stronger storm conditions. The strongest storm in the past two decades reached a DST of -500nT. We’re sitting at -100nT, which is a moderate storm.
With the prediction that things will intensify, keep your eyes on this event, especially if you’re watching for aurora!
This storm is especially exciting because it is the first storm that is being monitored by the Michigan Space Weather Modeling Framework running operationally at SWPC. You can see the SWMF predicted indices and maps of regional activity over at the SWPC website.