Dr Ying Zou | A New Type of Space Storm: The Extraordinary Auroral Event of April 2023

Space weather events can have dramatic effects on Earth’s magnetic field, potentially disrupting everything from power grids to GPS systems. Dr Ying Zou and her colleagues Dr Jesper Gjerloev and Shin Ohtani from Johns Hopkins University Applied Physics Laboratory led a groundbreaking investigation into an extraordinary disturbance in Earth’s magnetic field that occurred in April 2023. This unprecedented event is reshaping our understanding of how solar activity can trigger extreme space weather that impacts our technological systems.

Understanding Space Weather

Our planet’s magnetic field acts as an invisible shield, protecting us from the harsh effects of solar activity. This protective bubble, called the magnetosphere, usually deflects or redirects the constant stream of particles flowing from the Sun, known as the solar wind. However, when powerful eruptions occur on the Sun’s surface, they can temporarily compress and distort this magnetic shield, creating dramatic effects in the upper atmosphere.

These disturbances manifest in various ways. The most visible sign is the appearance of auroras – the spectacular light shows near Earth’s poles commonly known as the Northern and Southern Lights. But these atmospheric light shows are just the visible tip of a much larger phenomenon. The same processes that create auroras can also generate powerful electrical currents in the upper atmosphere, which in turn can induce unwanted electrical currents in ground-based infrastructure like power grids, pipelines, and telecommunications systems.

Scientists have long studied these space weather effects, categorising different types of magnetic disturbances based on their characteristics. Until now, they thought they had a good understanding of how these events typically unfold. But the extraordinary event of 24 April 2023 would challenge many of their assumptions.

A Remarkable Discovery

Dr Zou and her colleagues first noticed something unusual when examining data from magnetic sensors spread across the Arctic region. These instruments, which continuously monitor Earth’s magnetic field, recorded one of the most intense disturbances ever observed in the auroral zone – the region where space weather effects are typically strongest.

The numbers were startling. The event created electrical currents in the upper atmosphere that were much more powerful than those seen during normal storm conditions. Even more remarkably, these changes occurred with unprecedented speed. While typical magnetic disturbances develop gradually over tens of minutes, this event reached its peak intensity in just minutes.

Breaking the Pattern

As Dr Zou and her colleagues dug deeper into the data, they realised they had observed something that didn’t fit any known pattern of space weather activity. Traditional auroral disturbances, known as substorms, typically develop over one to two hours and affect a broad region of the upper atmosphere. They usually begin near midnight and spread both eastward and westward, eventually affecting a large portion of the polar region.

This new event was dramatically different. It lasted just five minutes and was concentrated in a surprisingly narrow band, only about 200–300 kilometres wide. Yet despite its narrow width, it stretched across nearly the entire night side of Earth, possibly extending even into the daytime region. Most surprisingly, it showed no signs of the usual eastward or westward expansion that characterises typical substorms.

The Detection Network

Understanding this unusual event required data from an impressive array of scientific instruments spread across the Arctic region. Dr Zou’s team analysed information from multiple satellite systems and ground-based instruments, each providing a different piece of the puzzle.

The SuperMAG network of ground-based magnetometers provided crucial data about the strength and location of the electrical currents. These instruments, spread across the world, measure tiny changes in Earth’s magnetic field. The team also examined data from satellites in various orbits, including the DSCOVR spacecraft at the L1 point – a special location between Earth and the Sun where the gravitational forces balance perfectly.

The THEMIS satellites, positioned in the magnetosphere, provided additional crucial measurements. Meanwhile, the AMPERE-NEXT system, which uses measurements from nearly 90 communications satellites, helped map the larger-scale electrical current systems in the upper atmosphere.

Unravelling the Mystery

By combining data from all these sources, Dr Zou’s team was able to piece together what had happened. They discovered that the trigger for this intense event was a brief but powerful surge in the solar wind. This surge compressed Earth’s magnetic field like squeezing a giant balloon, but in an unusually focused way that concentrated its effects in a narrow region.

The compression had a remarkable effect on the particles trapped within Earth’s magnetic field. It caused a sudden increase in the precipitation of electrons and protons into the upper atmosphere, creating an intense but short-lived band of auroral activity. This precipitation was different from the typical auroral displays seen during substorms, appearing as a diffuse glow rather than the more structured auroral forms usually observed.

Implications for Infrastructure

The discovery of this new type of space weather event has important implications for protecting our technological infrastructure. Most current warning systems and protective measures are designed around slower-developing storms, which give operators time to prepare and respond. The recognition that similarly intense effects can develop much more rapidly means these systems may need to be reconsidered.

The team’s measurements showed that the rate of change in the magnetic field during this event was extraordinarily high – reaching 914 nanoteslas per minute. This rate of change is particularly significant because, among other factors, it determines how strong the induced currents in ground-based infrastructure will be. The faster the magnetic field changes, the stronger these potentially damaging currents become.

A New Scientific Challenge

This discovery raises new questions about space weather and its effects on Earth. Dr Zou and her colleagues are now investigating whether similar rapid-onset events might have occurred in the past but gone unrecognised because scientists weren’t looking for this specific pattern of activity. The team is particularly interested in understanding what specific conditions in the solar wind might make such focused, intense storms more likely to occur. Their current hypothesis suggests that a combination of factors may be necessary, including a pre-existing period of strong solar activity followed by a sharp pulse in the solar wind pressure.

Looking ahead, Dr Zou’s team has identified several key areas for future research. They want to understand whether these events can be predicted with current satellite monitoring systems, and if new types of observations might be needed. They are also investigating whether similar events might occur in the Southern Hemisphere, and if they might have different characteristics.

The team is particularly interested in studying what processes in the magnetosphere create the large electrical currents in the atmosphere. During periods of high solar activity, magnetic fields, particles, waves, and instabilities all change in the magnetosphere, serving as multiple sources of disturbances in the atmosphere.

Protecting Our Technology in the Future

The research has practical implications for protecting our modern infrastructure. Power grid operators and others responsible for vulnerable systems need to understand the characteristics of these rapid-onset events to develop appropriate protective measures. This might include faster-acting automatic systems that can respond to sudden changes in magnetic fields before human operators can react. The timing of this discovery is particularly relevant as we approach a peak in solar activity expected in the next few years. During such peaks, which occur approximately every 11 years as part of the solar cycle, space weather events tend to become more frequent and more intense.

As our society becomes increasingly dependent on technologies vulnerable to space weather effects, understanding and predicting these events becomes ever more crucial. Dr Zou’s team continues to monitor for similar events, helping to build a better understanding of these dramatic space weather phenomena and their potential impacts on Earth. The discovery of this new type of storm serves as a reminder that space weather, like terrestrial weather, can still produce unexpected phenomena. As we continue to unravel the complex interactions between the Sun and Earth, each new discovery helps us better protect our technology-dependent society from the effects of our star’s more dramatic moments.