Can trigger auroras! What exactly is the origin of geomagnetic storms?

Audit expert: Zhan Mingjin

PhD, Chinese Academy of Meteorological Sciences

Some time ago, the news reported that the National Space Science Center of the Chinese Academy of Sciences detected a huge geomagnetic storm on Earth.

How big is this geomagnetic storm? It is the strongest geomagnetic storm so far in the 25th solar activity cycle. Under its influence, beautiful auroras can be seen in Xinjiang and Mohe, China.

Source: News Photo

In fact, a large geomagnetic storm was reported as early as March this year. Will the occurrence of multiple geomagnetic storms have any impact on our lives? What exactly are geomagnetic storms?

There are rumors that the Earth's magnetic field will reverse soon. What is going on? Let's take a look at the truth.

What is a geomagnetic storm?

Before answering this question in detail, we must first understand how the Earth's magnetism is generated.

The Earth's core consists of two parts: the inner core and the outer core. The inner core has the highest temperature and is solid; the outer core has the second lowest temperature and is filled with a large amount of fluid mainly composed of iron and nickel. These fluids are magnetic and will undergo convection under the action of the Earth's rotation and high temperature, causing electromagnetic induction and thus generating geomagnetism.

The Earth's magnetism has a history of at least 3.5 billion years. It extends through the Earth's interior into the universe, forming the Earth's magnetosphere, which can block the invasion of solar wind and protect the Earth's atmosphere and natural ecology.

Schematic diagram of the visual effect of the Earth's magnetic field Source: NASA Geomagnetic storms are global and violent disturbances of the Earth's magnetic field . They have specific intensity levels, and the Dst index is often used to grade them in research, while the Kp index is used to grade them in actual early warning applications. The highest Kp index is level 9, which is a very large geomagnetic storm level.

There are two types of solar explosive activities related to geomagnetic storms: solar flares and coronal mass ejections.

Solar flare is a phenomenon in which a local area of ​​the sun explodes violently, producing strong flashes. Based on the peak X-ray flux (wavelength between 100 and 800 picometers) measured by the GOES satellite near the earth, solar flares are divided into five levels: A, B, C, M, and X. Each level is further divided into 1-9 levels (except X level), and the highest value of X level has been recorded to be X-28.

When a solar flare occurs, a large amount of energy is released in a short period of time, generating a variety of high-energy electromagnetic radiation, such as gamma rays, X-rays, etc. These radiations reach the Earth and affect the Earth's ionosphere, interfering with the magnetic field; high-energy charged particles are also generated in the process, which also causes radiation interference.

Source: Baidu Encyclopedia

Coronal mass ejection (CME) is the phenomenon in which the corona on the surface of the sun ejects coronal material and plasma into interplanetary space.

These coronal materials and coronal hole high-speed plasma materials will hit the Earth's magnetosphere at speeds of hundreds of kilometers per second, causing significant compression and deformation of the magnetosphere, which in turn causes severe disturbances in the Earth's magnetic field and produces geomagnetic storms.

Source of Coronal Mass Ejection丨Baidu Encyclopedia

That is to say, the combined effects of solar flares and coronal mass ejections can lead to severe geomagnetic storms. The super-large geomagnetic storm mentioned in the news at the beginning of this article is a phenomenon caused by the combination of an M1.7-class flare and a full-halo coronal mass ejection.

Impact of geomagnetic storms

On Earth, the most direct impact of geomagnetic storms is the aurora .

When a geomagnetic storm occurs, charged particles in the geomagnetic field will enter the Earth's atmosphere along the magnetic field lines, causing collisions between atmospheric molecules and atoms to stimulate the production of "fluorescence", which is what we often call "aurora".

Source of the Southern Lights at Fox Glacier on the west coast of New Zealand's South Island in 2023 | Xinhua News Agency

Auroras mainly appear near the Antarctic Circle and the Arctic Circle. The closer to the equator, the rarer the auroras are in low and mid-latitude areas. Only when the intensity of the charged particle flow is large enough to produce a large geomagnetic storm under the action of the geomagnetic field, can the auroras be seen in low and mid-latitude areas. However, the auroras cannot be accurately predicted at present. You may stay in the Antarctic Circle for ten days or so, but you may not see the auroras.

Although the aurora is beautiful, geomagnetic disturbances can have adverse effects on many human activities, especially the communications industry.

The ionizing radiation emitted during a solar flare can interfere with the ionosphere of the Earth's atmosphere, causing ionospheric scintillation and ionospheric delay, which in turn can affect radio communications and GPS navigation and positioning systems, leading to positioning errors or interruptions.

In addition, geomagnetic storms can also cause induced currents in ground power grids, oil pipelines and other transportation lines, which can easily cause power grid tripping and other accidents. For example, in 1989, a large-scale power outage lasting 12 hours in Quebec, Canada was caused by a geomagnetic storm.

Geomagnetic storms can also affect the operation of spacecraft . Geomagnetic disturbances can cause changes in atmospheric density, which in turn increases atmospheric drag, causing the orbital height of satellites, especially low-orbit satellites, to drop, reducing the life of satellites.

The Skylab satellite was launched by the United States in 1973 and was expected to operate for 10 years. However, due to multiple geomagnetic storms, the satellite lost its stability after only four years and fell into the atmosphere in 1979.

Artificial satellite source: Baidu Encyclopedia

Geomagnetic storms can also affect the activities of some animals, such as homing pigeons and turtles, which rely on the geomagnetic field to sense direction. When the magnetic field becomes disordered, their movement and migration routes will change.

So, is there any way to detect the occurrence of geomagnetic storms in a timely manner?

Geomagnetic storm warning method

In 2021, China launched its first solar exploration test satellite, the Xihe , which can be used to observe solar atmospheric activities and provide early warning for geomagnetic storms so that timely preventive measures can be taken.

The Xihe spacecraft is equipped with a solar Hɑ imaging spectrometer, which can detect the Hɑ (hydrogen alpha) spectral line and scan and "take pictures" of the sun. The Hɑ spectral line is the strongest spectral line in the lower atmosphere that responds to solar activity. It can intuitively reflect the characteristics of the source area of ​​solar eruptions and help scientists correctly understand the physical mechanism of solar eruptions.

"Xihe" scanning image source丨National Space Administration

By analyzing the scanned images of the sun, scientists can understand the changes in atmospheric temperature, speed, etc. during solar eruptions, thereby building a complete physical model of the solar eruption process.

In 2022, Xihe successfully scanned the solar Hɑ-band spectrum for the first time. Currently, it only takes 46 seconds for Xihe to scan the entire solar disk, which is very efficient.

In addition, the National Space Weather Monitoring and Early Warning Center has also specially studied a set of satellite orbit forecasting methods, which comprehensively considers the impact of geomagnetic storms on satellites, allowing satellite forecasts to be carried out efficiently and orderly.

Some people worry that the frequent occurrence of geomagnetic storms will cause changes in the Earth's magnetic field. In fact, the Earth's magnetic field has been changing all the time . On average, the direction of the geomagnetic field reverses 4-5 times every million years, and each reversal lasts from thousands to tens of thousands of years.

Schematic diagram of the Earth's magnetic field Source: Baidu Encyclopedia

At present, there is no clear scientific research to prove the cause of geomagnetic reversal.

For human beings, there are still many secrets of the geomagnetic field that have not been discovered. With the continuous breakthroughs and developments in science and technology, I believe that in the near future, we will be able to unveil the veil of the geomagnetic field.