Craig Rodger and Lisa Evans, University of Otago

This essay appears in the catalogue for “Life in the Sun’s Atmosphere”, an exhibition of scientific photographs by Max Alexander exploring the impacts of space weather on human societies. It was launched at Lloyd’s of London on Tuesday, 4th of March, 2025.

There are very few ways humans can directly perceive the impact solar activity has on the environment around us, posing some interesting challenges for how we mitigate its effects on our planet, which can be dramatic. If you are particularly observant, you might notice unusual behaviour of species that use Earth’s magnetic field for navigation due to space weather, while the most impressive indication is the southern or northern lights, glowing and pulsating in the night sky.

Māori who settled on the North Island of Aotearoa New Zealand observed the southern lights, or Aurora Australis, and called it Tahu-nui-ā-rangi, or The Great Burning in the Sky. According to one story, the aurora was interpreted as the reflected glow from campfires lit by Māori ancestors who travelled south and were trapped on a land of ice, Antarctica. Seeing the aurora gave these North Islanders a feeling of connection to these explorers. More recently in 1882, a couple of decades after the historic Carrington Event, telegraph operators across New Zealand found their land lines and cables inoperable. In Auckland, watchmen apparently mistook the aurora for a fire, and the city’s fire bells rang out in alarm.

For the most part, however, space weather is invisible. This means that until humans started to develop technologies that could be negatively impacted by space weather, it largely went unnoticed. But today, we are more susceptible to the whims of the Sun than ever before, and no more so than the potential impacts on our power grids.

Voltage potentials

Huge explosions on the Sun can result in giant plumes of ionised gas called coronal mass ejections (CMEs). These are launched from the Sun’s atmosphere and travel through the heliosphere — the region of space around the Sun dominated by the solar wind that stretches out beyond Pluto. CMEs don’t always collide with Earth, but when they do, they have a big effect on our planet’s magnetic field. The impact of the CME compresses the magnetic field, squeezing it inwards on the dayside, while at the same time energetic electrons rain down near the poles and cause aurorae.

Large distortions in Earth’s magnetic field in space produce magnetic changes at our planet’s surface, creating “voltage potentials” across the landscape and making the ground behave like a battery. If we compare electrical current to water, a voltage potential is like an increase in water pressure in one place, which makes water flow to where the pressure is lower. Similarly, when there are higher and lower voltages across the landscape, electrical current will flow, depending on how conductive the landscape is. Different materials have different electrical properties such as soil, rock, minerals, and water, and this alters the size of the induced electrical currents.

Earth is often depicted as a giant bar magnet, with its north pole a little distant from the geographic north pole, and its south pole around Antarctica. In this representation, the Earth’s magnetic field runs from pole to pole, creating lines of geomagnetic latitude and longitude that don’t quite align with the geographic latitude and longitude that we’re familiar with. On a magnetic world map, New Zealand is situated in a region where the geomagnetic and geographic differences are large – with most of the South Island even further south magnetically than the southern-most tip of South America.

Electrical currents induced in power lines by geomagnetic storms are known as Geomagnetically Induced Currents (GICs), and their severity depends on all the factors mentioned above: the strength of the magnetic field, the direction of transmission lines, the conductivity of the landscape around the grid, the distance from large bodies of water, and the layout of the power system and its equipment. In New Zealand, our research team has a unique opportunity to study the conditions that lead to hazardous GICs, not just due to the geophysics research undertaken in New Zealand, but also thanks to a long-standing collaboration between research and industry.

Solar Tsunamis

On 6 November 2001, engineers at the New Zealand electricity network operator Transpower were alerted to a large geomagnetic disturbance when power grid alarms were triggered across the South Island. Within a minute of the storm commencing, a transformer at Halfway Bush substation near Dunedin failed.

This was not the first time a power grid had been badly affected by a large geomagnetic disturbance; in March 1989, circuit breakers on a power grid operated by Hydro-Québec in Canada were tripped by a large storm. That system’s very long transmission lines were built on top of the Canadian Shield, a geological feature that conducts electricity very poorly, making the power lines highly vulnerable to GICs as currents flowed along the path of least resistance. This caused a power failure across the entire province for more than nine hours.

Following the 2001 disruption, Transpower developed their first plan to mitigate the impacts of space weather on the New Zealand grid. Since this was still a very new field of inquiry, many assumptions had to be made by engineers at that time. For instance, they focused on the substations at auroral latitudes on the lower South Island, and on long transmission lines that cut across the direction of the Earth’s magnetic field, running in an East-West direction, where they believed the impacts would be largest.

In their search for more clarity around the space weather hazard, Transpower teamed up with our researchers in 2016 at the University of Otago in New Zealand to provide answers to a series of important questions. In an unprecedented collaboration between a power operator and research scientists, Transpower shared GIC observations collected by their measurement systems over almost two decades with our Solar Tsunamis research programme to study the impacts of extreme space weather events. Using this data, our researchers have been able to construct and empirically validate a detailed model of the New Zealand power grid, enabling us to study the past and present impacts on transformers during multiple large geomagnetic storms.

Daniel Mac Manus, then a PhD student at the university and now a postdoctoral researcher, used the new validated model to determine that the initial Transpower mitigation plan would reduce the impact of GICs in individual lower South Island transformers by up to 30 percent during large geomagnetic storms. However, the model also showed that one-in-200-year extreme storms would likely produce dangerous GIC levels in about 15 to 25 percent of all the main grid transformers. Importantly, hotspots were found throughout the Iength of New Zealand, not just for the latitudes closest to the pole.

In close collaboration with Transpower engineers, Daniel helped to design a new, more robust mitigation plan. We systematically examined predicted GIC levels in each transformer on the network and determined which power lines could be disabled without causing instability in the grid. By doing this, we were able to balance the need to “keep the lights on” against the risk of damage to vital equipment that would be very slow and difficult to replace. The result was a new mitigation plan, declared ready for operational use in 2023. Following on from that work, we are now investigating GIC hot spots in the grid identified by the model where blocking devices could potentially be installed to further increase the resilience of the New Zealand power supply.

Solar Tsunamis researchers from the Victoria University of Wellington have also been working closely with a major New Zealand gas pipeline operator to investigate the impact of GICs on their network. Engineers at the University of Canterbury have also been answering important questions about how transformers in the power network respond to GICs. And researchers at the GNS Science research institute have been filling in data gaps about the conductivity of the New Zealand landscape, as well as developing a real-time space weather “nowcasting” data stream from the Eyrewell Geomagnetic Observatory, allowing risk managers to monitor geomagnetic activity in New Zealand as it happens.

They have also digitised historic magnetic field data from New Zealand dating back to 1951, enabling our experts in statistics to experiment with methods for forecasting the timing and severity of geomagnetic storms. Our international partners at the British Geological Survey, British Antarctic Survey, and the University of Michigan in the US have also been lending their expertise to some of the big, cutting-edge questions about the hazard posed by space weather, and how to improve our resilience.

Another important part of our project has been the development of outreach and school engagement programmes by the team at Tūhura Otago Museum, aiming to increase public awareness of the issue. Similar to other natural hazards such as earthquakes and tsunamis, it is important for New Zealand communities to have a good appreciation of what geomagnetic storms are and how they impact society, so they can be prepared for a large event and respond appropriately when one occurs.

Testing the plan

On the wintry morning of Friday 10 May 2024, awareness was growing in New Zealand that a large geomagnetic storm was on its way. A series of solar flares and CMEs had begun a couple of days before, and space weather forecasters in the US had issued a Severe Geomagnetic Storm Watch for Friday evening – translating to Saturday morning in New Zealand. At least five of the CMEs were directed towards Earth, and there was still a chance that more solar activity could occur.

Throughout the day, various organisations in New Zealand monitored the situation, including Transpower. They watched for indications that their new mitigation plan should be put into action. The US Space Weather Prediction Center (SWPC) warned of a powerful storm early Saturday morning, a prediction that grew throughout the morning. With evidence of an imminent disruption to the power supply increasing, Transpower issued two Grid Emergency Notices by midday, and began to disconnect power lines as outlined in the mitigation plan.

Throughout that day engineers at Transpower were in active communication with myself and Daniel Mac Manus, seeking advice about how bad the storm was likely to get. While this was clearly a big – if not extreme – scenario, it was sensible to enact the switching plan for all of New Zealand, especially given there was a chance of more CMEs coming our way. However, it was thankfully nowhere near the one-in-200-year storms we had been preparing for.

Communications between our team and Transpower, along with other industry and government stakeholders, continued through the day, while media enquiries about the storm exploded. Interest developed into a frenzy by Saturday evening, when crowds flocked to view aurorae across New Zealand, all the way to the upper parts of the North Island. Social media was flooded with photos of the incredible multi-coloured display.

Transpower’s report after the event examined what went right over that weekend, and what lessons could be learned. Having the plan in place to manage the event, personnel on hand to take appropriate action in a timely manner, access to important real-time data, and experts from the Solar Tsunamis team available were all positives.

What didn’t go well? There was still a mixed level of industry understanding about the space weather hazard. Forecasting and nowcasting needs to be improved so power operators have as much warning of an event as possible. There are still questions to be answered around responding to much more severe storms, such as which transformers to take offline when conditions are rapidly worsening. And decision-making around when the storm had passed and circuits could be returned to service proved complex.

While we are on our way to answering the big questions about space weather and its impacts on power grids and beyond, there is still a lot more work to be done. Some of the work needs scientific research and some is about engineering solutions, while there are also operational, planning, and regulatory challenges to tackle.

Advanced technologies have become integral to modern life, but the more we depend on them, the more vulnerable we are to major disruptions to power and communications. Our programme shows this is a solvable problem. With the right information, the right tools, and widespread awareness of the hazard posed by space weather, we can work together to be prepared and build resilient systems. After that, we can sit back, relax, and enjoy the aurora the next time a major storm hits our planet.