Many more people around the world than usual have recently been able to see the Northern and Southern Lights overhead with the naked eye. This unusual event was caused by a very strong solar storm, which affected the movement of the Earth’s magnetic field.
The sun reaches its maximum point of activity in an eleven-year cycle. This means we can expect more explosive outbursts of particles. Under the right conditions, these are the factors that ultimately generate the beautiful auroras in the sky, as well as the geomagnetic storms that can damage infrastructure such as power grids and orbiting satellites.
So what is actually going on to cause these symptoms? The Northern and Southern Lights are usually limited to very high and very low latitudes. High-energy particles from the sun flow toward Earth, guided by the sun’s magnetic field. They are transferred to the Earth’s magnetic field in a process known as reconnection.
These very fast and hot particles then sprint along the Earth’s magnetic field lines – the direction of a magnet’s force – until they hit a neutral, cold atmospheric particle such as oxygen, hydrogen or nitrogen. At this point, some of that energy is lost – and this heats the local environment.
However, the atmospheric particles don’t like to be energetic, so they release some of this energy into the visible light range. Depending on which element is too hot, you’ll see a different set of wavelengths – and therefore colors – emitted in the visible light range of the electromagnetic spectrum. This is the source of the auroras we can see at high latitudes and, during strong solar events, also at lower latitudes.
The blue and purple hues in the aurora come from nitrogen, while the green and red hues come from oxygen. This specific process happens all the time, but because the Earth’s magnetic field is similar in shape to a bar magnet, the area activated by the incoming particles is at very high and low latitudes (Arctic Circle or Antarctica in general) .
What happened to allow us to see the aurora much further south in the Northern Hemisphere?
You may remember in school spreading iron filings on a piece of paper on top of a magnet to see how they positioned themselves in the magnetic field. You can repeat the experiment several times and see the same shape each time.
Earth’s magnetic field is also constant, but can be compressed and released depending on how strong the sun is. An easy way to think about this is to imagine two half-inflated balloons pressed together.
If you inflate one balloon and add more gas to it, the pressure will increase and the smaller balloon will push back. As you release that extra gas, the smaller balloon relaxes and pushes back out.
For us, the stronger this pressure is, the closer to the equator the relevant magnetic field lines are pushed, meaning auroras can be seen.
Exceptional storms
This is also where the potential problems arise: a moving magnetic field can generate current in anything that conducts electricity.
For modern infrastructure, the largest currents are generated in power lines, train tracks and underground pipelines. The speed of this movement is also important and is monitored by measuring how disturbed the magnetic field is compared to “normal”. One of these metrics used by researchers is called the disturbed storm time index.
By this measure, the geomagnetic storms of May 10 and 11 were exceptionally powerful. With such a strong storm there is a potential danger of generating electrical currents. Power lines are most at risk, but have benefited from the protection built into power stations. These have been in focus since the 1989 geomagnetic storm, which melted a power transformer in Quebec, Canada, causing hours of power outages.
A greater risk is metal pipelines that corrode when electrical current is passed through them. This is not an immediate effect, but there is a slow build-up of eroding material. This can have a very strong effect on the infrastructure, but is very difficult to detect.
Although currents are a problem on the ground, they pose an even greater challenge in space. Satellites have a limited amount of ground and an electrical surge can destroy instruments and communications. When a satellite loses communications in this way, it is called a zombie satellite and is often lost completely, resulting in a very large loss of investment.
The changes in the Earth’s magnetic field can also affect the light passing through it. We cannot see this change, but the accuracy of the GPS location system can be greatly affected as the location readout depends on the time passing between your device and a satellite. The increase in electron density (the number of particles in the signal’s path) causes the wave to bend, making it take longer to reach your device.
The same changes could also affect the bandwidth speed of satellite internet and the planet’s radiation belts. This is a torus of highly energetic charged particles, mainly electrons, located about 13,000 km from the surface. A geomagnetic storm can push these particles into the lower atmosphere. Here the particles can interfere with high-frequency (HF) radio used by aircraft and affect ozone concentrations.
Auroras are not limited to Earth; many planets have them and they can tell us a lot about the magnetic fields that occur on these celestial bodies. One specific device used to simulate auroras is a ‘planeterella’, first developed in the early 20th century by Norwegian scientist Kristian Birkeland.
A magnetic sphere (representing the Earth) is placed in a vacuum chamber and the solar wind is simulated by firing electrons at the sphere. We have two of these tools in the UK within universities and here at Nottingham Trent University I recently helped a student build a budget version as a masters project.
By changing the magnetic field strength and the distance between objects, you can observe how auroras change. The emissions are predominantly purple, as you would expect with an atmosphere of 72% nitrogen. A strong emission ring appears around the top, where the aurora would be seen on Earth, and this ring moves up and down in latitude depending on the magnetic field strength.
As a natural occurrence, auroras are a miracle. But even better, with every strong geomagnetic storm we make improvements that help protect against the potential damage from future events.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Ian Whittaker does not work for, consult with, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.