Extract from ABC News
Auroras were seen across most of Australia during the 2024 Gannon solar storm. (Supplied: Patrick Wayn)
In short:
The May 2024 solar storm, which was the biggest in two decades, squeezed one of Earth's protective layers to one-fifth its size.
This layer of charged particles — called the plasmasphere — dropped tens of thousands of kilometres during the storm, which allowed the aurora to be visible so far towards the equator.
What's next?
The proliferation of satellites since the last big solar storms has allowed scientists unprecedented new information on how these super storms work.
While last week's stunning auroras delighted many people around Australia, the solar storm that created them was not on the same level as one that happened last year.
The biggest solar storm of the past two decades, known as the Gannon or Mother's Day storm, lit up the sky in May 2024.
Not only did it dazzle the world for three days, it squeezed a layer of charged particles surrounding our planet known as the plasmasphere to a fifth of its size, according to a new study.
The study, published in Earth, Planets and Space, analysed data from the plasmasphere using Japan's ARASE satellite, as well as from the lower ionosphere using GPS receivers.
"Monitoring both layers showed us how dramatically the plasmasphere contracted and why recovery took so long," one of the researchers, Atsuki Shinbori from Nagoya University, said.
"This prolonged disruption can affect GPS accuracy, interfere with satellite operations, and complicate space weather forecasting."
The phenomenon also explained why auroras were seen as far north as Townsville and as far south as Florida last year.
The Gannon or Mother's Day Storm
On May 9, 2024 a sunspot caught the attention of solar researchers.
The sunspot, called AR3664, was 15 times the diameter of Earth, and rivalled the dimensions of an 1859 sunspot which led to the most extreme solar storm ever documented.
NASA's Solar Dynamics Observatory captured these images of the solar flares on May 8, 2024 (left) and May 9, 2024 (right). (Supplied: NASA/SDO)
The sunspot was facing Earth and released multiple large eruptions of plasma and magnetic energy, called CMEs, over a few days.
NASA's Solar Dynamics Observatory captured images of the two solar flares on May 10 and May 11, 2024. (Supplied: NASA/SDO)
The Earth is surrounded by multiple protective layers of charged particles called the magnetosphere.
One of these — the plasmasphere — extends up to 44,000 kilometres above the Earth, while the much lower ionosphere sits from around 1,000 km.
When the CMEs hit these layers, they disturb Earth's magnetic field and upper atmosphere producing dazzling displays of colour.
An aurora occurs when the sun's particles make their way through the Earth's magnetic field. (ABC News)
The storm, which hit around Mother's Day in many parts of the world, was classed an "extreme" G5 storm, the highest intensity on the G scale. The most recent storm last week was a G4.
It was the most powerful storm since the so-called Halloween storm in 2003.
The Mother's Day storm was later named the "Gannon storm", after space physicist Jennifer Gannon who died suddenly a few days earlier.
If you had good weather, skies of pinks and greens could be seen as far north as Uluru and Townsville.
The storm affected GPS, and also caused planes to divert and satellites to drop significant altitudes.
'Draining' the plasmasphere
Earth is currently seeing more intense auroras than usual as the 11-year solar cycle peaks.
The previous solar cycle, which occurred between 2009 and 2020, was particularly mild, so recent auroras are the biggest we've seen for about 20 years.
Since then, humans have blasted vast numbers of satellites into orbit, which has given scientists an unprecedented look at how these big solar storms operate.
Aurora australis over Hobart on May 11, 2024. (Supplied: Scott Glyph)
Brett Carter, a researcher in space physics and space weather at the Royal Melbourne Institute of Technology (RMIT), said the ARASE satellite was in the "right place at the right time" to track the plasmasphere as it shrunk over time.
Because the ARASE satellite orbits every 10 hours — shifting from 32,100 kilometres above Earth down to just 460 km — it had a prime time view of the days-long auroral display.
"The orbital configuration happened to be sweeping the right part of the magnetosphere in order to observe the the changes in the plasmasphere," Dr Carter said.
"It's a really cool paper."
During the solar storm the plasmasphere dropped from 44,000 km above Earth to just 9,600 km.
"When the storm hits, all these particles just get ejected out of the magnetosphere," Dr Carter said.
"It's like a flush on a toilet."
It was this drain of particles through the magnetosphere that caused such amazing auroras so close to the equator, as the ejected particles were able to travel much further along Earth's magnetic field lines.
Aurora australis turned the sky red over Walkaway in Western Australia on the morning of May 11, 2024. (Facebook: Katie Ann Thoars)
Getting back to normal was also extremely slow. The team found it took four days for the plasmasphere to spring back into shape — the longest recovery recorded since the ARASE satellite began monitoring the plasmasphere in 2017.
They suggested this was due to something called a negative storm, which is where the amount of plasma depletes radically.
"A negative storm means that the electron density in the ionosphere is depleted globally for several days," Dr. Shinbori said.
“The negative storm slowed recovery by altering atmospheric chemistry and cutting off the supply of particles to the plasmasphere."
"This link between negative storms and delayed recovery had never been clearly observed before."
The Gannon storm has provided scientists with a wealth of new information.
Late last year, researchers found the pink auroras seen over much of the world were caused by a mixture of oxygen, which glows red, and di-nitrogen, which glows blue.
Other research looked at the same solar storm on other planets, with researchers tracking the auroras across Mars a few days after they hit Earth.
"The last big storm we had was in the early 2000s," Dr Carter said.
"In this line of work, you get maybe two or three of these big ones in the span of your career.
"There are lots of people focusing efforts on this going forward — ourselves included."
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