If you’ve ever lived or spent a lengthy amount of time in the high North, you may have run into the Aurora a few times in your life – the beautiful pillars of pink, purple, green and everything in-between that sometimes can even be bright enough to cast shadows at night; but it wasn’t long ago that us low-latitude southern folk were treated to the spectacle.
From May 10th to May 13th, one of the strongest solar storms in recent memory brought Aurora visibility down as far south as Puerto Rico, with a big bullseye locally here in the Tennessee Valley – but what’s the mechanism behind this phenomena, anyways? What enabled the visibility of something so rare this far south? Let’s break it down…
It all starts with the fact that the sun has “cycles” of activity roughly every 11 years – and we’re currently in the upward swing of the most recent solar cycle. During the active cycles, sunspot activity increases dramatically; sunspots being areas of cooler plasma on the surface which indicates a highly active subsurface. It’s typical for CMEs and other flares to stem from these areas of sunspots due to their association with higher activity.
In fact, a CME is what was responsible for the Aurora we recently saw. But wait… what’s a CME?
A CME, or Coronal Mass Ejection, is exactly that – an ejection or eruption of the magnetic field of the sun and it’s attached solar mass/plasma. These CMEs are no slugs, either – the fastest of these ejections have been measured to haul along at more than 2,000 miles per SECOND. It should come as no surprise, then, that the impacts of these CMEs are something we on earth have to prepare for – though most are harmless and pointed away from us.
Sometimes, however, we end up right in the path – and we’ve seen what can happen in such a case. In 1859, what’s known as the “Carrington Event” occurred: the strongest geomagnetic storm in recorded history, associated with a CME, impacted earth, and the surge in the magnetic and electric fields actually physically shocked telegraph operators on the ground, and, just like our recent event, caused auroras to be visible as far south as Mexico.
It’s all this magnetic energy associated with these CMEs that causes the Aurora, in fact. All of that mass and energy isn’t a phantom force – it comes with very real, and very powerful (for their size) charged particles that have a lot of energy to give out to whatever they hit; and in our case, their target is the upper layers of our own atmosphere.
As a quick refresher, our atmosphere consists mostly of two elements – Nitrogen and Oxygen. Of course, we breathe and utilize oxygen biologically, but Nitrogen actually makes up more than 70% of the atmosphere by mass, and it’s the varying elements, alongside just how low or high up they are – that actually dictates the colors you see.
Let’s take our recent Aurora event for example – many of us across the country saw deep pinks and reds across the night sky, with some lingering greens to boot. This is no surprise, when considering that the deeper red hues are often associated with the most intense solar activity, due to the fact they’re at the same elevation as many satellites… and are associated with “excited” oxygen particles. Yes, it’s true – there’s oxygen even that high up!
The attached explainer graphic courtesy of the Canadian Space Agency breaks down the various atomic compositions and elevations of the Aurora that you may have seen – which, if you did, send us your photos. It never gets old!
All images in this explainer were sourced via the public domain (NASA, Wikipedia)
