Scientists are getting closer to being able to predict solar storms more accurately

Put simply, a solar storm seems to temporarily alter the ‘pattern’ of particles hurtling towards our planet. If we learn to interpret this trail, we can gain a better understanding of what is happening inside the storm itself and just how dangerous it might be for Earth.

The study has been published in the journal *Physical Review Letters*.

The scientists used data from the Chinese LHAASO observatory, one of the world’s largest cosmic-ray detectors.

What is a solar storm?

A solar storm is not just a bright flare on the Sun. Sometimes the Sun ejects a huge cloud of superheated plasma with a magnetic field into space. Such eruptions are called coronal mass ejections.

If such a cloud heads towards Earth, it can trigger a geomagnetic storm. Whilst this poses no direct danger to people on the planet’s surface, it can affect technology: satellites, radio communications, navigation, GPS/GNSS and power grids.

It is therefore important for scientists not only to observe that a solar flare has occurred, but also to understand exactly what is heading towards Earth: how strong the cloud’s magnetic field is, how it is structured, and what consequences it may have.

What do cosmic rays have to do with it?

Cosmic rays are highly energetic particles that reach Earth from space. They constantly collide with the upper layers of the atmosphere and create cascades of other particles. They can be detected using specialised detectors.

Until now, scientists knew that solar storms could affect relatively low-energy cosmic rays. However, it was thought that very high-energy particles should pass almost freely through the magnetic structures of solar storms.

New research has shown that this is not always the case. Even very high-energy cosmic rays can be slightly ‘affected’ by a solar storm. It is not that they disappear completely, but their flux becomes slightly irregular.

What the scientists observed

The team studied a solar storm that passed close to Earth on 4 November 2021. To do this, they used data from the LHAASO observatory in China.

LHAASO records hundreds of millions of cosmic rays per hour. The scientists looked not just at the total number of particles, but at the directions from which they were arriving. This is important: normal atmospheric changes can distort the overall flux, but they should not create a sustained ‘bias’ in direction.

And they did find such a bias. For several hours, fewer cosmic rays than usual were arriving from one part of the sky. The authors attributed this to the fact that the leading edge of the solar storm contained a region of strong magnetic turbulence. This scattered some of the cosmic rays and left a noticeable trace in the data.

In simple terms

Imagine that a ‘rain’ of cosmic particles is constantly falling towards Earth. Usually, it arrives almost evenly from all directions.

But when a solar storm passes between Earth and space, it seems to alter this ‘rain’ slightly. In one direction, there are fewer particles. It is like a shadow that the storm leaves in the stream of cosmic rays.

It is precisely this ‘shadow’ that scientists have learnt to detect.

Why this could help with forecasting

Today, solar storms are tracked using spacecraft and observations of the Sun. But there is a limitation: a satellite only measures conditions at the exact point where it is located.

Cosmic rays can provide a broader picture. They travel through large areas of space, so changes in them can reveal what is happening not just at a single point, but across a larger part of the solar storm.

If such observations are confirmed during other events, cosmic rays could become an additional early-warning tool. This would not replace satellites, but could complement them and help to assess the structure of a dangerous storm at an earlier stage. In the article itself, the authors state that this observation opens up the possibility of studying interplanetary magnetic structures using arrays of cosmic-ray detectors around the world.

Why this is important for Earth

Severe solar storms can disrupt the technologies on which modern life depends. NOAA warns that coronal mass ejections can trigger geomagnetic storms, disrupt GPS/GNSS, radio communications and satellites, and even induce additional currents in power grids.

Therefore, the task for scientists is not simply to know that ‘a storm is coming’, but to understand what form it will take. One storm may pass almost unnoticed, whilst another could cause serious problems for satellites and infrastructure.

This new method could help precisely with this: it provides a clearer view of the internal magnetic structure of a storm heading towards Earth.

Background

Solar activity is particularly important at present because humanity is increasingly dependent on satellites, navigation, communications and energy infrastructure. The more such systems there are, the more important it is to understand in advance how space weather might affect them.

LHAASO observations show that even very high-energy cosmic particles can act as a kind of ‘scanner’ for solar storms. This makes cosmic rays not only a subject of astrophysics, but also a potential tool for protecting Earth’s technologies.

Source

Study: Zhen Cao et al., “Transient Large-Scale Anisotropy in TeV Cosmic Rays due to an Interplanetary Coronal Mass Ejection”, Physical Review Letters, 2026. DOI: 10.1103/mkk2-hbq5. A preprint is also available on arXiv.