Major Aurora Alert

(SCOTTSBLUFF, Neb.) — Weather awareness is greater now than ever before. In fact, weather is one of the most popular topics ever in the history of the world, and a recent phenomenon has arisen like a Phoenix from the ashes.

We’re talking about the heightened prevalence of Northern Lights in places never even thought of until recently. Let’s take a look at a recent post by Christopher Matthews on the current geomagnetic storm.

By Christopher Matthews

THE NEW FORECAST IS OUT and it’s a corker.  Happy days are here again, but the nights could be even better.

NOAA calls for three days of storming from the recent coronal mass ejection (CME) triggered by Tuesday’s large X-class flare.  Note that the forecasters say they’ve run multiple simulations of the CME and have only “moderate” confidence in the timing of its arrival.  So: we know something is coming.  The “when” part is a little trickier.

NOAA releases three-day forecasts like the one below twice a day, at 0030 and 1230 UT. The forecast projects the anticipated highest average disturbance in Earth’s magnetic field for each three hour increment of the days being forecast, measured in units called Kp. For those new to aurora hunting: Kp is a planetary average of magnetic disturbances (K) registered at more than a dozen magnetic observatories around the world. Kp has a loose correlation to the strength of the aurora, but it more closely represents the latitudes in which the aurora can be seen.

In general, the higher the Kp, the further the aurora can be observed from the poles – assuming it is visible at all. In Iceland, for example, we can see the aurora even with very low Kp readings – Kp 3 or below would be just fine. But further south, say in Indiana, you would expect to need something higher – Kp 7 or better.

Because Kp is an average, your local K conditions can and will vary, in the same way that a category one hurricane might bring just as much rainfall to a specific neighborhood as a category five. The charts below merely indicate the general area in which the lights may reach at different Kp levels. There is no substitute for actually going outside and seeing for yourself!

The NOAA forecasts predict the maximum expected intensity of the weather for a given block of time. This particular forecast’s prediction of Kp 7 does not mean the forecasters expect continuous storms during the indicated times; it means, for example, that the forecasters expect Kp 7 conditions to be reached at some point between 2100-midnight (UT) on 4 Oct 24.  If you need help converting Universal Time to your own timezone, you can use this tool: https://dateful.com/convert/utc

Forecasts, of course, are only that: predictions based on observed events near the Sun that may affect the Earth’s magnetic field. As a storm approaches, we will get more and better data from satellites close to the Earth – but not until about 30 minutes to an hour before it actually hits. Until then, this is the best we’ve got.

Why is it difficult to track storms – particularly CMEs? A coronal mass ejection is usually triggered by a visible event on the surface of the Sun, like a flare or a filament eruption. We also can see the debris from the event as it heads out into space – billions of tons of insanely-hot plasma makes for an impressive show.

But we can only see the CME for a few hours. It cools rapidly, and as it moves away from the Sun, the reflected light from our favorite star fades as well. The shockwave attenuates as it crosses the 150 million km or so from the Sun to the Earth. Complicating matters, the satellite we rely on mostly for these observations is rather old – it’s now almost 27 years beyond its intended mission end. So we sometimes don’t get all the observational data we like.

Once a CME leaves the vicinity of the Sun, we can’t see it. CMEs are magnetically charged, and as they pass through space, they can be deflected by the magnetic fields close to the Sun, and by the interplanetary magnetic field. Small changes in trajectory can add up over the two to four days of time required to travel from Sun to Earth. So the models used to predict the impact of a CME are necessarily imprecise. And sometimes, just wrong. The Earth is a very small target compared to the vastness of space.

We have little to no additional data until right before the CME lands … or doesn’t land. Shortly before a storm reaches the Earth, it sweeps across a small flock of satellites about 1.5 million km (roughly 1 million miles) Sunward from the Earth. These measure solar wind characteristics, providing data with odd names like Bz, Bt, p/cc, and so on. For a primer on these, take a look at this post: https://www.facebook.com/groups/northernlightsalert/posts/6046882492079513

The NOAA forecast is like your local meteorologist’s extended weather forecast – useful for planning purposes, but sometimes the rain doesn’t show up on time. Satellite data is like the sound of the rain hitting your roof: a pretty accurate indicator that the storm is here, but not great for planning your aurora hunt. You have to balance both.

So – this forecast predicts good times ahead, but we’ll need to watch the real-time solar wind data as it comes streaming in, too.  And of course, that’s exactly what we’ll be doing, and reporting, here.  Good luck, and happy hunting!