by Recently, many more people around the world than usual have been able to see the northern and southern lights above them with the naked eye. This unusual event was triggered by a very strong solar storm, which disrupted the movement of the Earth’s magnetic field.
The Sun is reaching peak activity in an 11 year cycle. This means we can expect more explosive bursts of particles. In the right circumstances, these are what 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 really going on to cause these phenomena? The Northern and Southern Lights are usually confined to very high and very low latitudes. High-energy particles flow from the Sun towards Earth, guided by the Sun’s magnetic field. They are transferred to the Earth’s magnetic field in a process called reconnection.
These extremely fast and hot particles travel down the Earth’s magnetic field lines – the direction of force from a magnet – 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 up the local environment.
However, the atmospheric particles do not like to be energetic, so they release some of this energy in the visible light range. Now, depending on the element that is overheated, you will 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 see at high latitudes and, during strong solar events, at lower latitudes as well.
The blues and purples in the aurora come from nitrogen, while the greens and reds come from oxygen. This particular process happens all the time, but because the Earth’s magnetic field is shaped like a bar magnet, the area that the particles are energized into is at very high and low latitudes (generally the Arctic or Antarctic circle) .
So what happened to allow us to see the aurora much further south in the northern hemisphere?
You may remember at school cracking iron filters on paper on top of a magnet to see how they behave with the magnetic field. You can repeat the experiment and see the same shape each time.
The 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, adding more gas, the pressure will increase and push the smaller balloon back. As you release that extra gas, the balloon relaxes less and pushes back out.
For us, the stronger this pressure, the closer to the equator the relevant magnetic field lines are pushed, which means that auroras can be seen.
Exceptional storms
This is also where the potential problems come in: a moving magnetic field can generate a current in anything that conducts electricity.
In terms of 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 tracked by measuring how perturbed the magnetic field is from “normal”. One such measure used by researchers is the storm disturbance time index.
By this measure, the geomagnetic storms of 10 and 11 May were extremely strong. With such a strong storm, there could be a risk of electrocution. Power lines are most at risk, but they benefited from protections built into power plants. These have been in focus since the 1989 geomagnetic storm that melted a power transformer in Quebec, Canada – causing occasional power outages.
Metallic pipelines are more prone to corrosion when an electric current passes through them. This is not an immediate effect, but a slow build-up of corrosive material. This can have a very strong impact on infrastructure but is very difficult to detect.
While currents are a problem on the ground, they are an even bigger challenge in space. Satellites have a limited amount of ground in them and electrical surges can destroy instruments and communications. When a satellite loses communication in this way, it is called a zombie satellite and is often lost completely – resulting in a very high loss of investment.
The changes in the Earth’s magnetic field can affect the light that passes through it. We can’t see this change, but the accuracy of a GPS-style positioning system can be greatly affected, as position readings depend on the time it takes between your device and a satellite. Due to the increase in electron density (the number of particles in the signal’s path), the wave bends, meaning it takes longer to reach your device.
The same changes can also affect satellite internet bandwidth speeds and the planet’s radiation belts. These are a torus of highly energetic charged particles, mostly electrons, about 13,000km 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 – they have plenty of planets and can tell us a lot about the magnetic fields of those celestial objects. A particular piece of apparatus used to simulate auroras is a “planeterella”, developed by Norwegian scientist Kristian Birkeland in the early 1900s.
A magnetic sphere (representing the Earth) is placed in a vacuum chamber and the solar wind is simulated by shining electrons onto the sphere. We have two of these instruments 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 strength of the magnetic field and the distance between objects, you can observe how auroras change. The emission is mostly purple, as you would expect in a 72% nitrogen atmosphere. A strong emission ring is visible around the top, where the aurora would be seen on Earth, and this ring moves up and down in latitude depending on the strength of the magnetic field.
As a natural event, auroras are amazing. But it’s even better that with every strong geomagnetic storm, we make improvements that help protect against potential damage from future events.
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Ian Whittaker does not work for any company or organization that would benefit from this article, does not consult with, shares in a company or organization that would benefit from this article, and has not disclosed any material relationships beyond their appointment academic.
