Recently, more people around the world have been able to see the northern and southern lights with the naked eye than usual. This unusual event was triggered by a very strong solar storm that affected the movement of the Earth’s magnetic field.
The Sun reaches its maximum activity point in an 11-year cycle. This means we can expect more explosive particles to be shed. Given the right conditions, they create beautiful aurora borealis in the sky as well as geomagnetic storms that can damage infrastructure such as power grids and orbiting satellites.
So what’s actually going on to cause these phenomena? The Northern and Southern Lights are generally limited to very high and very low latitudes. High-energy particles from the Sun flow towards Earth, guided by the sun’s magnetic field. They are transferred to the Earth’s magnetic field in a process known as reconnection.
These really fast, hot particles then hurtle along the Earth’s magnetic field lines (the direction of the magnet force) until they hit a neutral, cold atmospheric particle like oxygen, hydrogen, or nitrogen. At this point some of the energy is lost, which heats the local environment.
But atmospheric particles do not like to be energetic, so they release some of this energy in the visible light range. Now, depending on which element is very hot, 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 can see at high latitudes and at lower latitudes during strong solar events.
The blues and purples in the aurora come from nitrogen, and the greens and reds come from oxygen. This particular process occurs all the time, but since the Earth’s magnetic field is similar in shape to a bar magnet, the field energized by incoming particles is at very high and low latitudes (the Arctic Circle or Antarctica in general).
So what happened in the northern hemisphere that allowed us to see the aurora much further south?
In school, you might remember scattering iron filings on a sheet of paper above a magnet to see how they aligned with the magnetic field. You can repeat the experiment multiple times and see the same shape each time.
The Earth’s magnetic field is also constant, but can be compressed and released depending on the strength of the Sun. An easy way to think about this is to imagine two half-inflated balloons pressed together.
If you inflate a balloon by adding more gas, the pressure will increase and push the smaller balloon back. When you release this extra gas, the little balloon relaxes and gets pushed back.
From our perspective, the stronger this pressure is, the closer the relevant magnetic field lines move to the equator, meaning auroras can be seen.
extraordinary storms
This is also where potential problems arise: A moving magnetic field can produce 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 tracked by measuring how much the magnetic field is distorted from “normal”. One such measure used by researchers is called the distorted storm time index.
By this measure, the geomagnetic storms of May 10 and 11 were extraordinarily strong. There is a danger of electrical currents occurring in such a strong storm. Power lines are most at risk but benefit from protections built into power plants. These have been a focus since a geomagnetic storm in Quebec, Canada, in 1989 that melted a power transformer and caused a power outage for hours.
Metal pipelines that corrode when electric current passes through them are at greater risk. This is not an instantaneous effect, but a gradual accumulation of eroded 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’re an even bigger problem in space. Satellites have a limited amount of grounding, and a power surge could damage devices and communications. When a satellite loses communications in this way, it is referred to as a zombie satellite and is often lost completely; This results in a very high investment loss.
Changes in the Earth’s magnetic field can also affect the light passing through it. We cannot see this change, but since the location reading depends on the time elapsed between your device and the satellite, the accuracy of the GPS-style location system can be greatly affected. Increasing the electron density (the number of particles in the signal’s path) causes the wave to bend, meaning it takes longer to reach your device.
The same changes could also affect the bandwidth speed of satellite internet and the planet’s radiation belts. They are a donut of high-energy charged particles, mostly electrons, about 13,000 km from the surface. A geomagnetic storm can push these particles into the lower atmosphere. Here, particles can interfere with the 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 on these celestial bodies. One particular apparatus used to simulate auroras is the “planeterella,” which was first 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 firing electrons at the sphere. We have two of these tools at universities in the UK, and here at Nottingham Trent University I recently helped a student create a budget version as a Masters project.
You can observe how auroras change by changing the magnetic field strength and the distance between objects. The emission is mostly purple, as you would expect in a 72% nitrogen atmosphere. A strong emission ring appears at the peak on Earth where the aurora is visible, and this ring moves up and down in latitude depending on the magnetic field strength.
As a natural phenomenon, aurorae are spectacular. But even better, with each strong geomagnetic storm we make improvements to help protect against 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, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic duties.