On December 1, Heilongjiang Daxinganling, Mohe City is now a gorgeous aurora. Courtesy of Visual China.
During this time, "Aurora" swiped the screen.
At around 19:00 on December 1, Beijing time, Mohe, located in the northernmost part of China, once again had an obvious aurora. Since then, the second aurora on record has also occurred in northern Beijing, and the aurora phenomenon has been found for the first time in many places in Erguna City, Inner Mongolia......Many netizens asked: What causes the Aurora to often appear in Mohe this year, and what causes the Aurora to "patronize" a relatively low-latitude area like Beijing?
To put it simply, the main reasons can be summarized in two aspects: first, the position of the earth's magnetic poles is gradually drifting in the direction of Russia and China, and second, there are frequent strong magnetic storms this year.
What is the magnetic pole?The magnetic poles are the north and south poles of the earth's magnetic field. The Earth's magnetic axis (i.e., the imaginary straight line connecting the north and south poles of the Earth's magnetic field) has an angle to the Earth's axis of rotation, which results in most auroras occurring near the geographic poles, but not around the geographic poles. Interestingly, the angle between the Earth's magnetic axis and the axis of rotation is not fixed, which means that the geographical location of the magnetic pole can change. Areas near magnetic poles are generally more prone to aurora phenomena.
Since the beginning of the 21st century, the magnetic pole position of the northern hemisphere is crossing the polar region from the direction of Canada and gradually drifting eastward towards Russia and China, which means that when a magnetic storm occurs, the probability of seeing the aurora in China will be higher than before. If you want to know when you can see the aurora, you can pay attention to the geomagnetic storm forecast. When a very strong geomagnetic storm is expected, there is a high probability that the aurora will be visible. Of course, for now, it is easier to see the aurora in the higher latitudes of our country.
The "magnetic storm" mentioned above refers to a global violent disturbance of the Earth's magnetic field, usually caused by a solar storm, which causes the sun to eject high-energy, supersonic material. The process of "strong magnetic storms" is as follows: after the high-energy, supersonic material reaches the earth, it will compress the earth's magnetic field, causing the disturbance of the earth's magnetic field, so that if the matter has a southward magnetic field (that is, the opposite direction of the earth's magnetic field), it will cause more violent disturbances. The "hair dryer blowing hair" can be used as an analogy to the process by which a solar storm ejects material to reach the earth: when we blow our hair with winds of different temperatures and speeds (corresponding to solar matter of different energies and speeds), the degree to which we feel the wind blowing our hair (corresponding to the degree of magnetic field disturbance) is different.
The poet Qu Yuan used the image of "dragon" to describe the aurora in "Tianwen", vividly called it "candle dragon", and asked "If the day is not good, how can the candle dragon shine?"."It means that where the sun can't shine, how does the aurora light up?Now we already know that the material emitted by the sun reaches the earth with a magnetic field, causing the earth's magnetic field to disturb violently, causing more energetic particles to enter the atmosphere in the polar regions along the magnetic field lines, and stimulate the atmospheric molecules and atoms to shine through collisions, which is the aurora.
It is worth mentioning that mid-latitude aurora is mostly red, not the common green in our impression, but these two colors of aurora are produced by the electron transition within the oxygen atom, so what causes them to be different in color?In fact, the energy of the oxygen atom is different from the altitude in which it is located. The mid-latitude aurora is located at an altitude of 250 km-400 km, while the polar aurora is located at an altitude of about 100 km, which also makes the energy of the mid-latitude aurora lower than that of the polar aurora, and the energy is inversely proportional to the wavelength, so the wavelength of the mid-latitude aurora is longer than that of the polar aurora, that is, from the green light with a shorter wavelength to the red light with a longer wavelength. Green can be seen in the aurora that appeared in Mohe on December 1, which largely indicates that the geomagnetic storm event was very strong.
The aurora is beautiful, but the magnetic storm event behind it poses a huge threat to human production and life. In the "Luancheng County Chronicles" of the Qing Dynasty, there is a record that "red gas originated in the northwest", which corresponds to the "Carrington Incident" in September 1859. According to historical records, the "Carrington Event" caused 8 days of severe space weather. Fortunately, human society at that time mainly relied on steam engines and manpower, and there was no radio communication and power transmission network, so the "Carrington Incident" did not bring too serious disasters to the earth.
But in modern times, this is no longer the case – one night in March 1989, the entire power grid in Quebec, Canada, was paralyzed by intense aurora activity, plunging the province into darkness and cold for nine hours. At the same time, the communication satellites of the United States and Japan were abnormal, and the global radio communication signals were greatly interfered with. Although this event was not as strong as the "Carrington Incident", it had a greater impact on human life. It is estimated that if the "Carrington Affair" were to occur today, the economic damage it would directly result could be in the trillions of dollars.
Although the geomagnetic storm event is far less intense than the "Carrington event", it may also increase the error of satellite navigation equipment and enhance the polar radiation, which will lead to an increase in the risk of transpolar flight, and may even affect the activity of carrier pigeons. From this point of view, seeing the strong aurora in the mid-latitudes may not be as "beautiful" as it seems to our daily lives.
The author is a Ph.D. student at the Institute of Geology and Geophysics, Chinese Academy of Sciences
Wu Jingyi, China Youth Daily.
*: China Youth Daily.