But as we know, auroras all appear in high latitudes. Why do aurora appear in East Asia at low latitudes?
On this issue, let's first briefly understand the principle of aurora.
There is a huge magnetic field around the earth, and the magnetic poles are located near the geographical north and south poles. The sun will release high-energy charged particles (plasma) at an extremely fast speed to form the solar wind. When these charged particles reach the earth, they will be deflected to the poles by the earth's magnetic field and then enter the upper atmosphere about 80 kilometers from the surface.
High-energy particles from the sun collide with molecules in the earth's atmosphere. As the main components in the atmosphere, oxygen and nitrogen bear the brunt. When oxygen and nitrogen atoms absorb energy, electrons will be excited. Because of instability, electrons will return to the ground state, emit green light and red light, and produce gorgeous aurora.
In most cases, the charged particles generated by the sun will be guided to the poles by the geomagnetic field, so the aurora can only be seen at high latitudes (10 degrees to the geomagnetic pole of 20 degrees).
However, at some time, the sun will explode on a large scale, producing strong flares and releasing super solar storms. When these large-scale high-energy charged particles reach the earth, it may lead to aurora in the sky at low latitudes.
For a long time, the carrington event of 1859 has been regarded as the most violent super solar storm known. At that time, astronomer Carrington found large-scale flares and sunspots on the sun. A large number of high-energy particles are released at a very high speed. They can reach the earth in less than 18 hour, which is more than three times faster than the ordinary solar wind.
This solar wind triggered geomagnetic storms on the earth, resulting in aurora in many parts of the world. People even saw the aurora light up the sky at 20 degrees north latitude. The incident also led to the failure of the wireless telegraph system, and the telegraph tower caught fire, which made it impossible to send and receive radio waves normally.
Astronomers at Osaka University in Japan found [1] through research that there was a stronger super solar storm before. According to Japanese ancient paintings and documents, red light appeared over Kyoto for 9 consecutive days in 1770. The sunspots recorded at that time showed that the size of sunspots was much larger than usual, indicating that the sun was very active at that time.
It can be seen that the red light of that year was the aurora caused by the super solar storm. The aurora lasted nine days, while the carrington event only lasted two days, which means that the super solar storm 250 years ago was even bigger.
Although the super solar storm was very strong, it had no effect on people at that time. However, if this incident happens today, it will cause extremely serious consequences, and the power grid and communication will be severely hit. The estimated loss will exceed 14 trillion yuan.
However, astronomers estimate that the super solar storm of that scale was very rare in that year, and it only happened once every five centuries on average, which means that the probability of happening once every 100 years is 1/5. It's been 16 1 year since the last solar eruption. In the future, we need to continue to pay attention to the dynamics of the sun and be alert to the destruction of modern human civilization.
Reference [1] Pian Gang Long Wu, Qing Jian Yan Qiao. 17 oblique zenith aurora over Kyoto in September 1770: graphic evidence of extreme magnetic storms, space weather, 20 17, 15,1314-1322.