Text | Liu Yong (Researcher, National Space Science Center, Chinese Academy of Sciences)
Aurora photographed at the Mutianyu Great Wall. Gao Jianming/photo
On the evening of May 10 and the early morning of May 11, under the influence of geomagnetic storms, rare auroras appeared in many places around the world, which was also a wide range of aurora seen in the mainland.
At 9 a.m. on May 11, the National Space Weather Monitoring and Warning Center issued a red alert for geomagnetic storms. While the aurora is a feast for the eyes, it also raises concerns – some say it causes power outages, others say it causes headaches, and others say it increases the incidence of cardiovascular disease.
Why has solar activity been particularly high lately? What causes geomagnetic storms? What are the effects of geomagnetic storms on people's daily lives?
It's all the "fault" of the solar cycle
It can be said that this is the cyclical "fault" of the sun's changes. Solar activity is related to the number of sunspots on the surface of the sun. In high years, solar activity is high and a large number of sunspots appear on the surface, while in low years, the frequency of solar activity and the number of sunspots are reduced. Solar activity varies roughly in an 11-year cycle, from low years to high years, and then back to low years.
Scientists define the low solar year of 1755 as the first year of the solar cycle, and this year is exactly the high year of the 25th solar week, and there are quite a few sunspots on the sun. Sunspots are essentially active zones and are also the source of solar activity, resulting in a series of violent bursts, some of which strongly disturb the Earth's magnetic field, forming magnetic storms and auroras.
It should be noted that solar activity is a quasi-periodic activity, which does not strictly follow the 11-year cycle, and the number of sunspots and the frequency of activity are not the same at the peak of each solar cycle. According to the pattern of past variation, around 2007, the 23rd solar week should end and enter the ascendant of the next solar week. Surprisingly, solar activity remained low between 2007 and 2008 and only slowly rose until 2009. The entire 24th solar week was very depressed, and around 2014 was the peak year of this solar week, but there were not a few major solar eruptions, let alone strong geomagnetic storms.
In general, in the 20 years from the end of the 23rd solar week to the last two years, due to the cyclical changes in solar activity and the sluggishness of the 24th solar cycle, we have hardly seen strong solar activity, nor have we seen strong geomagnetic storms, especially super magnetic storms caused by successive eruptions like the recent ones.
What causes magnetic storms? Why the aurora
Many people think that geomagnetic storms caused by flares are really the case?
Flares are the brightness enhancement of local areas on the surface of the sun, and before entering the space age, the solar eruptions that humans can observe from ground-based telescopes are flares, and scientists have also noticed that the 11-year cyclical changes in the frequency of flare activity coincide with the frequency and periodic changes in the occurrence of geomagnetic storms, so many people have come to this wrong conclusion that flares cause geomagnetic storms. However, there has been no good explanation for how flares cause geomagnetic storms.
It wasn't until the Sun and the Heliospheric Observer Satellite (SOHO) were launched into the sky that many flares erupted and the Sun ejected a large amount of plasma, known as coronal mass ejections, at the same time as the Sun was observed to erupt into the sky. After rounds of scientific arguments, scientists have finally come to the conclusion that coronal mass ejections are another form of solar eruption. The culprits responsible for geomagnetic storms have finally stood in the center of the stage of solar activity and become the focus of space weather research.
The sun is a fireball, and there is strong magnetic activity and magnetic field distortion in the active area near the surface of the sun, which contains a large amount of magnetic field energy. Coronal mass ejections and flares are caused by the energy released by a distorted magnetic field, which is the release of energy in the form of light, and these distorted magnetic fields can throw a large cloud of coronal mass due to drastic structural changes. Although coronal ejective material weighs hundreds of millions of tons, its main component is plasma, which is composed of protons and electrons, which is very thin, so it is huge, and the weight of a mass of ejective plasma the size of the Earth is the weight of two or three adults. However, due to its rapid speed and the magnetic energy contained in it, if the mass of material hits the geomagnetic field of the protective cover outside the earth, it will cause a strong geomagnetic disturbance.
Severe magnetic storms are more likely to trigger a combination of coronal mass ejection events, which are formed by the superposition of several coronal mass ejection events. Adjacent coronal mass ejections fuse together to form a larger projectile, often referred to as cannibal CME in English, which translates to "cannibal mass ejection", which is actually a coronal mass ejection assembly. The magnetic storm was triggered by the fusion of several successive coronal mass ejections accompanied by the flare, so the forecast result was a super magnetic storm.
The aurora is also often talked about because of its beauty. Essentially, the aurora is the product of high-energy particles hitting the atmosphere. Think of the atmosphere as a phosphor screen, where high-energy particles emit light when they hit it, and different atmospheric components emit different colors of light. The pink aurora we see from Xinjiang is the light of oxygen atoms at a height of hundreds of kilometers. In true high latitudes, green aurora lights are often seen, emitting from relatively low altitudes.
There are two different sources of energetic particles that form auroras, solar energetic particles produced by solar eruptions, and particles in some space near Earth that are accelerated by the magnetic storm itself. Therefore, the aurora occurs before the magnetic storm, and the aurora becomes an early warning of the magnetic storm, and it will appear throughout the process of the magnetic storm.
How to look at geomagnetic storms rationally
Magnetic storms can affect the health of two groups of people, astronauts on the space station and passengers on polar flights. In addition, the impact of magnetic storms on human health is basically negligible, although there are a few scientific studies that claim to find evidence that magnetic storms cause cardiovascular disease, but it is not widely accepted by the academic community. Even the change in magnetic field caused by a super magnetic storm is less than 1% of the change in the strength of the magnetic field on the ground, and it is difficult to imagine that such a small change in magnetic field will affect life activities. Of course, the energetic particles that accompany magnetic storms may affect life near Earth, but only only on life on the Earth's surface. We have never heard of a significant increase in the incidence or mortality of a disease caused by magnetic storms, nor have we seen similar incidents in our own lives.
Magnetic storms are most affected by satellites, spacecraft, and equipment in space. For example, magnetic storms can cause the atmosphere to rise and the orbit of satellites to decay, which directly leads to shorter satellite lifetimes. The energetic particles produced by magnetic storms can electrify satellites, affect the normal operation of instruments and equipment, and even cause the entire equipment to be broken down and burned in severe cases. In 1998, there was a GALAXY communication satellite failure caused by a magnetic storm. The mainland has also reported cases of damage to some space equipment due to magnetic storms.
In certain cases, magnetic storms can affect transmission lines and even cause large-scale power outages. The 1989 power outage in Quebec, Canada, was triggered by a super magnetic storm. However, this usually occurs at high latitudes, and it is relatively rare for most of the continent to be in the middle and low latitudes.
Solar flares can also affect ionospheric and shortwave communications. However, the phones we use every day are in the mode of fiber optic plus base station, which is usually not affected by magnetic storms or solar flares.
Of course, because solar flares affect the ionosphere, ionospheric disturbances caused by magnetic storms can have an impact on navigation signals. Usually during a magnetic storm, the navigation signal is corrected accordingly so that navigation can proceed normally.
Such magnetic storms have also been very rare since humans had a complete geomagnetic record. Now that we have a very complete space and ground observation system, and the Meridian II interplanetary scintillation monitoring telescope hosted by the National Space Science Center of the Chinese Academy of Sciences has just been built, researchers will use the relevant data to conduct in-depth research on such solar eruptions and geomagnetic storms, and look forward to more exciting results, so that we can have a clearer understanding of the process of solar storms affecting the Earth's space environment.
In addition, although we do not have to worry about the direct damage caused by geomagnetic storms to the body, it is still recommended that everyone pay attention to the news in time to understand the progress of magnetic storms while enjoying the beautiful aurora, so as to avoid secondary injuries or economic losses caused by geomagnetic storms damaging space equipment.