Space Weather at Climate & Space

Another Storm Watch!

Here we go again! NOAA SWPC has issued another storm watch for a G3 level geomagnetic event.  Right now, we’re already at G2 level.  My guess is that we’ll hit G3 if the interplanetary magnetic field turns southward, so keep an eye on the real-time solar wind conditions.  Because the storm has already started, I doubt that this will drive any visible aurora over the United States- by the time nightfall hits, the storm will have subsided again.  But keep your eyes peeled just in case.

Check out my previous storm watch post for an idea of what values to watch as the storm progresses.

Storm Post Mortem – Oct. 13, 2016 Event

Happy Monday.  Let’s take a look at the storm that started Thursday and had potential to reach a G3 level on NOAA’s geoactivity scale.  Click for a larger version:

NOAA SWPC real time solar wind values (top four frames) and observed and predicted Kp and Dst indices (bottom two frames, respectively.)
NOAA SWPC real time solar wind values (top four frames) and observed and predicted Kp and Dst indices (bottom two frames, respectively.)

The outstanding feature in the solar wind during this storm is the long period (near 18 hours!) of southward Interplanetary Magnetic Field (IMF).  This is seen in the red line in the top frame starting shortly after Oct. 13th and lasting into the next day.  Southward IMF conditions are when the solar wind most efficiently transfers energy to the magnetosphere and Earth’s atmosphere, so the storm looks promising on these terms alone.  IMF BZ (the component of the field that is oriented north- and southward, shown in the red line in the plot) reaches a value of almost -30nT!  Values of -10nT are good enough to give us a strong response on the ground; -30nT is approaching what we would expect during a very strong storm.

Now, let’s jump down to the bottom two frames, which show the geomagnetic activity indices KP and DST.  The former is an index of the global space weather activity at Earth and ranges from 1 to 9.  The latter is an index of how much energy is stored in the “ring current” of the magnetosphere, a region that extends out to around 8 Earth radii (around 28,000 miles altitude.)  The more negative DST, the more energy stored.  In my previous post, we had hoped that this storm would intensify from “G2” to “G3” status, or a KP of 7 from 5 or 6; DST had already reached -100nT as I frantically typed.  Unfortunately, my post came during the maximum of activity: both DST and KP recovered after that point.  These are moderate values; this is a typical and relatively uninspiring event.  Browsing the community-driven aurora monitoring website, Aurorasaurus, there is evidence of a light show reaching the northern United States, but not much further south than that.

So what happened?  This is a time where the southward IMF values needed a little more help from the solar wind.  The solar wind was relatively slow for a space weather storm (yellow line), staying around 400-500 km/s.  During strong events, we expect much faster values- 600, 800, or even 1000 km/s.  Next, we want a dense solar wind- tens of particles per cubic centimeter.  When the IMF was southward, the solar wind was the least dense: <10 per cubic centimeter.  The IMF was just right, but it didn’t get the help it needed to make this a very exciting space weather storm.

Finally, in the bottom frame, we see a strange discontinuity in the predicted DST as it jumps from -125nT back to zero.  We see a similar jump in the KP plot.  What could’ve happened here?  This is a cold restart of the Space Weather Modeling Framework- something went wrong, and the code needed to be restarted from scratch.  The problem could have happened anywhere in the predictive chain: in the processing of real-time solar wind data, a hardware glitch in the supercomputing environment, or an issue with the SWMF software itself.  This is disappointing, but not completely unexpected- the real-time simulations at SWPC are brand new, and we – the researchers and code developers at the University of Michigan as well as the team at NOAA – will use this event to make the entire system more robust for future storms.

As a scientist, this storm will still be important.  Every storm gives us an opportunity to make new observations of the sun-Earth system.  With our sparse and ever-changing fleet of satellites taking measurements, each storm has the potential for something new to be discovered, even if it is not a record-setting event.  This storm is one of the few that has happened in the lifetime of the young Magnetosphere Multi-Scale (MMS) satellite mission, so I expect some exciting observations to come from that.

Space Weather Alert!

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.

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