Solar flares and storms have the potential to damage satellites, knock down power grids, and—as seen this weekend—trigger bright auroras.
Solar activity is closely linked with the number of sunspots, or bundles of magnetically charged plasma, which can collide, shear, and snap, sending strong radiation out in all directions. In extreme cases, entire bundles of charged particles—called coronal mass ejections, or CMEs—can be shot out in one direction. If these bundles are aligned with Earth's magnetic field, they can cause additional damage.
Sunspot numbers wax and wane over an 11-year solar cycle. The US National Oceanic and Atmospheric Administration (NOAA) has forecast the solar maximum will peak in 2024, making flares and coronal mass ejections more likely. The Bureau of Meteorology operates the Australian Space Weather Forecasting Centre, which issues space weather alerts for the public and industry.
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How do solar flares and CMEs impact us on Earth?
Dr Mark Cheung, Science Director, Space & Astronomy, explains:
"Solar storms can manifest as solar flares, which are enhancements in ultraviolet and x-ray radiation. Once emitted, the radiation takes about eight minutes to reach the Earth. The energetic radiation can ionise atoms in the Earth's upper atmosphere and cause it to puff up. This can cause radio communications blackouts, errors in global positioning systems, and increase drag on satellites, changing their orbits.
"Some, but not all, solar storms are also accompanied by coronal mass ejections (CMEs), which are bundles of magnetised, ionised material hurtling through space as fast as a few thousand km per second. If directed toward Earth, they may arrive within a day or take a bit longer depending on their speeds. Some CMEs have a magnetic field directed southward, which is particularly disruptive to the Earth's own magnetic field.
"The Earth's own magnetic field acts like a shield, partially protecting us from the impacts of CMEs and the ambient solar wind. But when a strong CME hits, the Earth's magnetic field rings like a bell, manifested as geomagnetic storms. This can cause anomalous currents over long distance electrical cables and pipelines, posing threats to critical infrastructure such as power grids. On the plus side, geomagnetic storms are often accompanied by beautiful aurora in the north (Aurora borealis) and in the south (Aurora australis). Sometimes, as on 11-12 May, the aurora can even be witnessed from mainland Australia.
"Some flares and CMEs are also accompanied by particles accelerated to near the speed of light. These travel along the superhighways that are magnetic fields connecting the Sun and Earth. Deposition of these particles on satellites can degrade their components, including solar panels and sensitive instruments." 
What causes solar flares and CMEs?
Dr Mark Cheung, Science Director, Space & Astronomy says:
"Solar flares and CMEs are caused by magnetic activity on the Sun. Sunspots are actually planet-sized bundles of strong magnetic fields (as strong as in MRI machines). These sunspots are being churned by plasma flows beneath the surface of the Sun."
Dr John Morgan, Space Weather Scientist, explains:
"Magnetic field lines have a special fundamental property – they typically cannot cross each other. This means that as they get twisted and tangled they store energy like a wound up spring. When a so-called "magnetic reconnection" occurs, these fields relax rapidly, which can release explosive energy out into space."
Can we expect more auroras and solar storms in 2024?
Dr Mark Cheung, Science Director, Space & Astronomy, explains:
"It's impossible to say exactly when the solar maximum will peak, but we are tracking several sunspot clusters, including those responsible for the recent auroras.
"Space weather forecasters monitor the Sun, solar wind, and space environment constantly, and offer forecasts of varying certainty from around 24 hours to 30 minutes in advance. Skywatchers should monitor the Bureau of Meteorology's Space Weather Forecasting Centre, and the Space Weather Prediction Center, to find out about any upcoming activity."
Dr John Morgan, Space Weather Scientist, says:
"No-one can know for sure. The events of the last few days certainly seem to be some of the most significant of the smartphone era. It's certainly possible that we've just seen the peak of auroral activity for this solar cycle. However, experience tells us that big events can happen even well after the peak of the solar cycle, so for those who missed out, there's certainly a good chance of comparable events happening over the next few years."
Can we predict when solar storms are going to occur?
Dr John Morgan, Space Weather Scientist, explains:
"This is a hugely difficult problem and a big area of active research covering everything from predicting if/when large solar flares are likely to occur, through to improved tracking of events as they travel from the Sun to the Earth.
"Aurora chasers should understand that predicting solar storms is currently much more uncertain than predicting conventional weather, and there are a lots of reasons for this. One big difference is an extra variable: the magnetic field of the storm. This is both important to how the storm impacts the Earth, and very difficult to measure remotely.
"Another problem is that once we see an event happen on the Sun, we have very little ability to track it as it travels towards the Earth. Often the first definitive information that we have is when storm reaches a cluster of satellites that we have parked up-stream of the Earth towards the Sun. Among other things, these satellites measure the speed of the solar wind, and the size of the southward pointing magnetic field. These give a very good indication of what is heading towards us, however they only give us about an hour's notice.
"CSIRO along with national and international partners is actively working on novel ways to track storms on their way to Earth, as well as trying to measure their magnetic field remotely."
