Aurora lights up the sky in Mercer, Auckland. Photo: Supplied / Laura Acket
Transpower has restored the circuits it took out of action over the weekend, because of concern they could be damaged during the solar storm.
The national electricity system turned several circuits off on Saturday, ahead of a geomagnetic storm hitting. There were concerns the solar storm would damage satellites and power equipment.
"We have been monitoring the solar storm as it was escalated on Saturday in terms of its impact from severe to extreme, and took action to - in terms of a contingency plan - to switch out some transmission circuits to protect things like transformers and also generators connected to the grid," Transpower executive general manager of grid development John Clarke told Morning Report on Monday.
"Earth has been pelted with the effects of the solar storms. That's moving the magnetic fields that protect the Earth around, and actually induces electric currents through the Earth and long transmission lines."
Transpower says grid emergency is over after solar storms
People around the world enjoyed colourful auroras, caused by material being spat out of a huge spot on the sun. The stunning, colourful lights, or Aurora Australis, it generated were clearly visible around the country.
"It was probably the best display of the aurora I've seen in my time in New Zealand, and it's certainly the most powerful storm since 2003," Otago Museum director and astronomer Dr Ian Griffin told Morning Report, adding it could be seen in the northern hemisphere as far south as Florida.
But as pretty as they are, aurora are just a harmless side effect of the Earth being bombarded with electrically charged particles, which can really mess with electrical systems.
In 1859, the 'Carrington Event' "took out the internet at the time, which was the telegraph system", Griffin said.
The world is much more connected now than it was 160 years ago.
"It was a thing called a coronal mass ejection (CME) - actually it was seven," James Barr from Trillium Technologies told RNZ's First Up.
"This is when the sun sort of expels a big chunk of ionised matter, which it does all the time, but of course, this time the Earth was in the way. And that's essentially what happened, is that we passed through this big chunk of ionised matter that was expelled from the sun."
Interaction with Earth's protective magnetic field creates the shape of each aurora, the particles lining up with the poles.
"All those photons collide with oxygen and nitrogen in the upper atmosphere, and it creates that sort of fluorescence effect. And when you see a sort of a deep red, that's sort of oxygen in the higher atmosphere, and when it's green, that's oxygen in the lower atmosphere.
"And then when it's a pink and a purple, that's nitrogen. That's why you get these beautiful colours."
Transpower extended the notice on Sunday to early Monday, when further activity was notified. It said all affected circuits came back online at 4am without any problems. There were no power cuts.
"There were some really significant spikes through some of our transformers but not quite at the level you might have expected," Clarke said. "So, you know, we took good, prudent action. It's paid off. No consumers lost power.
Otago University physics Professor Craig Rodger told RNZ that despite the storm reaching G5 - the top of the National Oceanic and Atmospheric Administration (NOAA) SWPC scale for geomagnetic storms - it had only just done so.
It was the largest such solar storm for more than a decade in New Zealand - but not as big as those of 2003 or 2001, and he said we had learned a lot since then.
Griffin said a few months ago, "some of Elon Musk's satellites for StarLink were taken down by the reaction of Earth's atmosphere to a solar storm".
More intense solar storms could occur in coming weeks
"So while they can be incredibly beautiful, they are also a threat to life on Earth and we really need to understand more about them. And that's why you know, scientists across the world are studying them.
"Solar tsunami as they're called, you know that they're coming, but you don't always know how powerful they are. So we get maybe two to three days' warning."
We were not off the hook yet, either.
"This particular storm is probably dying away, although there's a chance there might be some more tonight [Monday] and tomorrow night . But… we're heading towards a period of solar maximum when the sun is really active. There are lots of sun spots, and that means over the next few weeks and months I'm hoping to see a few more auroras like this."
Clarke said what they learned this weekend will help avoid disaster in future space weather events.
Freezing nights set to end
MetService meteorologist John Law said the minus 7 experienced in some inland parts of the country at the weekend would also have been "perfect for some astronomy".
Cold snap over, but frost for some
Sunday night was not as cold although inland parts of Canterbury with areas such as Mt Cook down to minus 2 degrees Celsius and the North Island's Central Plateau would have been chilliest.
Christchurch residents would be waking to "a touch of frost" but nowhere near as cold as last Friday which delivered a minus 6 start to the day.
Cloudier, wetter weather would be on the cards in the next few days, Law said.