What is the principle of aurora formation?

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Aurora is a unique atmospheric luminescence phenomenon in the North and South Poles. Aurora has left a beautiful figure in the myths and legends of the East and the West. With the development of modern science, human beings can look at it with a rational eye and make a scientific explanation.

For a long time, the genetic mechanism of aurora has not been satisfactorily explained. For a long time, people have always thought that aurora may be formed by the following three reasons. One view is that the aurora is a fire outside the earth, because the Arctic is close to the edge of the earth, so this kind of fire can be seen. Another view is that the aurora is the glow reflected by the red sun and the west. There is also a view that polar regions are rich in ice and snow. They absorb sunlight during the day, store it, and release it at night, which becomes aurora. In short, opinions vary and there is no conclusion. It was not until the 1960s that the physical description of the aurora was gradually formed by combining the ground observation results with satellite and rocket sounding data.

Now people realize that the aurora is related to the large-scale interaction between the earth's upper atmosphere and the geomagnetic field, and to the high-speed charged particle flow emitted by the sun, which is usually called the solar wind. It can be seen that the atmosphere, magnetic field and solar wind are indispensable conditions for the formation of aurora. Other planets in the solar system with these three conditions, such as Jupiter and Mercury, will also produce auroras around them, which has been proved by practical observation.

The geomagnetic field is distributed around the earth and wrapped by the solar wind, forming a rod-shaped colloid, which is scientifically called magnetosphere. To be more visual, let's make an analogy like this. The magnetosphere can be regarded as a huge TV picture tube, which gathers the solar wind particles entering the upper atmosphere into a beam and focuses it on the geomagnetic pole area. Polar atmosphere is the screen of CRT, and aurora is the moving image on TV screen. However, the TV screen here is not 18 inch or 24 inch, but the polar high-altitude atmosphere with a diameter of 4000 kilometers. Usually the audience on the ground can only see L/50 of the picture somewhere. In the TV picture tube, the electron beam hits the TV screen, because the screen is coated with luminescent substances, which will emit light and display it as an image. Similarly, when an electron beam from space enters the polar upper atmosphere, it will excite molecules and atoms in the atmosphere, leading to luminescence, and people will see the image display of aurora. In a TV picture tube, a pair of electrodes and an electromagnet act on the electron beam to produce and form a moving image. When auroras occur, the display and motion of auroras are caused by the modulation of particle beams by the changes of electric and magnetic fields in the magnetosphere.

Aurora is not only an optical phenomenon, but also a radio phenomenon, which can be detected and studied by radar. It also radiates some radio waves. It is also said that aurora can make all kinds of sounds. Aurora is not only an important topic in scientific research, but also directly affects many practical engineering projects such as radio communication, long cable communication, long pipeline and transmission line. Aurora also affects climate and biological processes. Of course, aurora also has many unsolved mysteries.

Aurora is considered to be one of the most beautiful wonders in nature. If we fly over the earth's north and south poles in a spaceship and look at the earth from a distant space, we will see a shining halo around the earth's magnetic pole, which is the so-called aurora egg. Because they are a little squashed on the side facing away from the sun and slightly elongated on the side facing away from the sun, they present an egg-like shape. Aurora eggs are constantly changing, sometimes bright and sometimes dark, sometimes extending to the equator, and sometimes shrinking to the extreme. The halo at midnight is widest and brightest. The statistical results of long-term observation show that the highest frequency of aurora appears in two annular regions near the north-south magnetic latitude of 67 degrees, which are called the Southern Aurora and the Northern Aurora respectively. Aurora activity occurs almost every day in the aurora area. In the inner area surrounded by aurora eggs, it is usually called polar coverage area. In this area, the aurora appears less frequently than in the aurora area with lower latitude. In the middle and low latitudes, especially near the equator, the aurora rarely appears, but it does not mean that the aurora cannot be observed at all. At the night of 1958 and 10, you can see unusual aurora in the tropics, which appears bright red. This kind of aurora is usually associated with extremely large solar flare bursts and strong geomagnetic storms.