Space Weather: What is it and Why We Should Know About it
The Sun is the closest star to us at about a distance of 150 million kilometres. Its energy is generated by nuclear fusion, from which high energy photons are produced. The interior layers of the Sun are the Core, the Radiative zone and the Convection zone, while the Photosphere, the Chromosphere and the Corona make up the Solar atmosphere.
Before we can talk about Space Weather, we need to understand about the Sun’s magnetic field. While the solar magnetic field is complicated, to simplify, we can say that like Earth, the Sun too has a north pole and a south pole. Until 1908, the fact that Sun has a magnetic field was not known. It was discovered by George Ellery Hale. He showed that the Sunspots on the solar surface have very strong magnetic field.
Sunspots are the most prominent features on the surface. The number of Sunspots vary with time in a cyclic manner, i.e., they increase and decrease in a 11-year cycle with some variation, which is called a solar cycle. This was first observed by Heinrich Schwabe. If we were to plot the positions of sunspots against time, we get a butterfly diagram.
It is pretty clear that as the number of sunspots vary, the magnetic fields will vary as well. While a sunspot itself is a short-lived feature, producing short term variations, the solar cycle or activity and dynamo processes are responsible for long-term variations.
So, what is a dynamo? Simply put, it is the process that generates and keeps the Sun’s magnetic field alive. The convection zone being as hot as 2 million degrees Kelvin, enables more elements to hold on to greater number of electrons. But this is hot enough to separate atoms into electrons and nuclei to form plasma, a state of matter containing electrically charged particles. The plasma at the bottom of the zone is extremely hot, which bubbles to the surface and loses its heat to space and then sinks back down. This constant movement causes the electrically charged particles to move as well, thus giving rise to electrical currents. However, it is known that electrical currents generate magnetic fields (Ampere’s law), which in turn generate electrical currents (Faraday’s law) and hence a feedback loop, called the dynamo, is formed. As long as this loop is uninterrupted, the Sun will continue producing magnetic fields.
These magnetic fields are so energetic that their effects can be felt all over the solar system, and accompanying them is a small amount of plasma. This stream of plasma is called as the Solar Wind, which makes up the Space Weather. Note that the plasma is released from the uppermost layer of solar atmosphere, the Sun’s corona.
But the flow of plasma is turbulent, which generates a magnetic field that isn’t uniform and the field lines are in random directions as well. These field lines often cross or tangle with each other, which can cause two types of explosions:
- an explosion where the magnetic fields explosively realign, releasing massive amounts of energy into space. It can create a bright flash of light, called the Solar flare, or
- an explosion which pushes solar matter into space, propelled forward in a single, preferential direction, called the Coronal Mass Ejection (CME).
Sometimes, the solar flares are accompanied by CMEs. The above illustration shows the difference between the two. The solar flare is seen as the bright flash, and the CME is seen as a loop of solar mass on the right limb of the Sun.
The solar flares are usually above the sunspots, and travel at the speed of light, and some of the energy released also accelerates very high energy particles which can reach Earth in tens of minutes. Based on their brightness in the X-Ray wavelengths, solar flares are classified into three categories:
- X-Class flares are big and can trigger radio blackouts around the whole world, and long-lasting radiation storms in the upper atmosphere.
- M-Class flares are medium-sized, which generally cause brief radio blackouts that affect the Earth’s polar regions, and minor radiation storms.
- C-Class flares are small with few noticeable consequences here on Earth.
The CMEs on the other hand travels slower from about 250 km/s to about 3000 km/s. These too usually take place from areas associated with sunspot groups. Usually, they can cause no harm to living beings on Earth, due to the Earth’s upper atmosphere, specifically the magnetosphere. The plasma from the CMEs is usually deflected by the magnetosphere to the poles, causing a phenomenon called the aurora. Earth’s magnetic field is “peeled open like an onion allowing energetic solar wind particles to stream down the field lines to hit the atmosphere over the poles,” as NASA puts it. But they can however disrupt satellites, radio communication and seriously injure or kill astronauts.
As with the case of any weather, most of the times, things are fine. They pass by without us (the commoners) noticing. But sometimes, solar super storms happen (once or twice a century). If it were to happen, we would first observe a strong solar flare, while the CME would hit us later. As it arrives, it would compress the Earth’s magnetic field, transferring energy to the magnetosphere. If the magnetic field of the CME and the Earth were to align in the right way, they merge causing the Earth’s field to elongate. Once the energy becomes too much to contain, it snaps like a rubber band, causing the energy to be directed towards Earth. This is called a Geomagnetic storm.
Since magnetic fields can generate electric currents, a high energy geomagnetic storm can potentially induce power in the power grids, which could either shut it down completely, or even destroy the transformer stations. We have some clue of what could happen, due to the severe storm witnessed in 1989. The effects were felt most in Quebec, Canada, where the power grid went offline for hours, depriving 6 million people of electricity immediately (for some, it took days to come back on).
But this wasn’t the worst storm we have witnessed. The biggest storm to have been recorded happened in 1859, called as the Carrington event. So strong that the currents coursed through telegraph wires, shocking any telegraph operator in contact with the device. It even caused the papers in the telegraph offices to catch fire. This wasn’t the only effect felt. The next morning before sunrise, as NASA quotes, “skies all over planet Earth erupted in red, green, and purple auroras so brilliant that newspapers could be read as easily as in daylight.” The auroras were visible even near some of the tropical latitudes.
A Carrington-level storm just missed the Earth in 2012. If it were to hit us now, it would be nothing short of catastrophic. It would inflict serious damage onto all electronic systems globally. An estimate suggested that the storm could cost all of humanity about 1–2 trillion USD in the first year, while it could take anywhere between 4–10 years for full damage recovery.
The experts are torn between the effect being just temporary blackouts and the scenario given above. We cannot be sure about it until it happens. The probability of such an event is estimated to be 12% per decade. But there’s more.
A star as calm as our Sun could create super flares every few thousand years, which are stronger than all the storms we have observed, even stronger than a Carrington-level storm. Their result could be more catastrophic. Humanity now heavily dependent on technology, would be thrown into darkness; which means loss of all electricity, electronics, communications and navigation. While temporary blackouts may not affect us significantly, a long-drawn outage would render supply systems, hospitals, and all other essential systems to fail. It is even expected to deplete the ozone layer significantly, which would result in increased risks of cataracts, skins cancer and such. The absence of power will make it further difficult to rebuild things. An estimate puts it between a few years to decades.
But it is not something to panic over. These scenarios are most likely to happen only when we are unprepared or ignore the warnings. While the storms themselves aren’t preventable, we can avoid their effects to a large extent.
Scientists have tool to predict solar cycle changes, which is to see the change in sunspot numbers. Since both flares and CMEs can be associated with sunspots, a prediction can be made to some degree of accuracy. Hence, when a storm is created, scientists have a few hours to few days to see a CME coming towards the Earth. While all the engineers may not know of the risks posed by solar storms, they can be informed as soon as the threat is assessed. Transformers and power grids can be taken offline to have preventative blackouts until the storm passes. Along with this, opening up more lines to dissipate the extra power would help as well. But most importantly, newer and robust upgrades to all grids and equipment would enable preparing for storms much easier.
While the Sun is very beautiful and provides us with everything we need to survive, it can also create something that is deadly. It is our job to be prepared for any possible event in order to survive.
References and suggested reading
Suggested YouTube video: Could Solar Storms Destroy Civilization? Solar Flares & Coronal Mass Ejections
Originally published at https://www.sciencenstuff.com on August 6, 2020.