Solar storms and space weather

The sun is constantly ejecting matter. A so-called solar storm occurs when activity on the sun becomes so intense that particles form electromagnetic fields which are thrown at high speed towards earth.

Two types of solar storms

Solar storms can be either coronal mass ejections or electromagnetic radiation bursts, known as solar flares. Coronal mass ejections cause geomagnetic storms, which are disturbances in the earth’s own magnetic field. This can disrupt electricity supplies. Solar flares can cause problems for radio communications and the GPS system.

Solar flares are large explosions on the sun’s surface that occur near sunspots. Particles accelerate and emit radiation that can reach earth. Coronal mass ejections are large clouds of plasma containing free electrons and protons that are ejected from the sun’s outermost layer (the corona).

Solar flares can reach earth quickly. Coronal mass ejections usually reach earth within three to four days. However, the vast majority of coronal mass ejections curve off and pass by the side of earth’s protective magnetic field.

Consequences of solar storms

In extreme cases, solar storms can disrupt electricity supply and electronic communications, and cause problems for train and air traffic.

When electrical currents caused by solar storms pass through high-voltage power lines, railway signalling systems and oil and gas pipelines, they are called geomagnetically induced currents.

In the electricity grid, induced currents can cause power lines and transformers to disconnect and may even damage them. This can result in temporary or long-term power cuts. Disruptions to electronic communications are mainly caused by prolonged power cuts but can also occur when currents are induced in the copper wires of the telecommunications network, which damages equipment.

Solar storms can also affect train traffic, as induced currents cause signalling faults. Air traffic may be affected by disruptions to radio communications and GPS systems.

Forecasts and warnings

Space weather forecasts are based on data from satellites and ground stations. The US satellite ACE (Advanced Composition Explorer) measures, amongst other things, the speed and density of the solar wind, as well as the direction of the magnetic field as it passes the satellite. Using this information, a geomagnetic storm can be predicted around half an hour before it occurs.

Measurement data from the satellite is collected by NOAA in the US and can then be downloaded by space weather warning centres (RWCs). The data that has been collected enables each centre to make its own forecasts. In Sweden, this task is carried out by the Institute of Space Physics in Lund.

In some cases, it is possible to monitor solar activity up to a month before a solar storm occurs, making it possible to issue warnings well in advance of any potential disturbances.