Aurora Australis: Rare geomagnetic storm 'likely' to put on another spectacular show over New Zealand skies

A rare geomagnetic storm caused a spectacular sight right across the country at the weekend, lighting up the night sky in pink, purple and green hues. 

If you somehow missed it, despite incredible shots taking over TV screens and social media, Otago University physics Professor Craig Rodger told AM that there's another "likely" chance you'll get to see it this week - but it all depends on where you are and if weather plays its part.  

"At the moment there is a forecast from the NOAA Space Weather Prediction Center that another coronal mass ejection is likely to occur maybe tonight, maybe in the next 24 hours. It's one of those areas that is actually quite difficult to forecast accurately when the coronal mass ejections will arrive," Prof Rodger told AM on Monday. 

"So there is another possibility. I would be surprised, I would be very surprised if it was a good as good as Saturday night though.  

"If you live in the lower South Island, I'd be saying there's a reasonable chance of aurora. If you live in the upper North Island, I really hope you saw it on Saturday, because it could literally be another ten years before we get a show that good." 

Christchurch. Photo credit: Supplied / Angela Cadogan

Where's the best place to view? 

Metservice meteorologist Mmathapelo Makgabutlane told Newshub those in the west and upper South Island will be the best places to see an aurora on Monday night. 

That's those on the West Coast and Buller region, as well as those in Marlborough and Tasman areas. 

Inland Otago and Southern Lakes areas are looking "okay", so Makgabutlane said "some spots could be lucky". 

However, for those in eastern parts of the South Island it's looking "pretty cloudy" which could spoil the view - that's those in Canterbury, Southland and Dunedin. 

But while it sure was a sight to see at the weekend, Transpower issued a grid emergency notice that was extended to 8pm Sunday. 

The notice was a precaution over solar storm activity which could interfere with New Zealand's electricity supply. 

What are we really seeing in our beautiful night skies? 

"Well, it turns out that there was a series of explosions on the sun which threw out a bunch of material out into space," Prof Rodger explained.  

"We call that a coronal mass ejection, or popularly known as a solar tsunami, and that material was directed towards the Earth. So it took about a day and a half to travel from the sun to the Earth, and then it started crashing into our magnetic field.  

"That energises the magnetic field of the Earth, boosts up the aurora so it's brighter and more dynamic and interesting. But most importantly for us, moves that aurora away from Antarctica towards New Zealand." 

The colourful event started about 5am on Saturday.  

"Of course, most of us didn't see that because, you know, we were still in bed and it took a while before the sun came up. But by the time the sun went down on Saturday night, it was still blasting away. And so we had the chance to see the aurora," Prof Rodger said. 

"Coronal mass ejections strike the Earth quite often but this was such a big one."  

It was declared by the United States NOAA Space Weather Prediction Center as a G5 class storm - the strongest level of geomagnetic storm.  

The last one of those was in October 2003 - so 21 years ago.  

"In terms of the New Zealand magnetic field, we haven't seen anything like this for over 25 years," Prof Rodger said. 

Whangārei. Photo credit: Supplied / Greg Campbell Wedding Photography

Why is it clearer through a phone lens than our eyes? 

"The amazing, progress in technology, basically. Modern phone cameras and high-quality cameras are more sensitive than our eyes and so it can pick out more detail and get the colours better," Prof Rodger explained. 

Those capturing the spectacle had to hold still to get the perfect shot, though, including one wedding photographer who made his newlyweds in Whangārei kiss for 13 seconds to a crisp aurora backdrop. 

But everyone's photos appear different in both colour and movement. 

What makes the aurora look different? 

"The aurora is literally different colours," Prof Rodger said. 

"The particles that are penetrating very deeply, and by deeply I mean maybe 120km altitude, that causes the atmosphere to glow in colors like green, but the slightly less energetic is arriving at a higher altitude, more like 200km, maybe 250km, and up there the atmosphere glows red." 

Dancing around himself on AM, Prof Rodger said the movement we see is because the aurora is made up of charged particles, electrons and protons. 

"They're guided by the magnetic field of the Earth but the magnetic field of the Earth is very, very disturbed because we're having this big storm and that causes the particles to be moving around and therefore the lights to be drifting." 

Dunedin. Photo credit: Supplied / Sam Oldham

Is there any health or technology risk? 

But don't worry, Prof Rodger explained that to be "zapped" by any sort of radiation from the geomagnetic storm someone would have to be up "really high". 

He added that the Transpower notice was issued in "extremely large magnetic storms". 

"This would be an example of an event that was large enough to be a little bit concerned about, but not large enough to cause a really serious impact because the magnetic field is changing.  

"There's a physics law called Faraday's law, which says that a changing magnetic field will induce currents on the electrical conductor. The electrical network is just this huge collection of conductors so we end up with currents being induced in the network which aren't meant to be there.  

"About two years ago, Transpower and one of my students and I helped develop that plan that they enacted on Saturday to shut down some of their transmission lines, remove them from service to decrease the size of those currents and thereby help protect our network." 

Thankfully, in this event the electricity supply was not impacted. 

Prof Rodger said there's "probably not" any reason for concern about explosions on the sun. 

"It's been happening for billions of years and we seem to have got away with it," he said. 

"I mean, there are issues in terms of the possible impacts on our technology, and it's an area that we are learning more about both in New Zealand and across the world. These are such big phenomena that they're global phenomena.  

"But it's not something that keeps me, you know, awake at night that there are explosions on the sun. The sun is just this amazing, huge burning ball of gas."