To give a clear picture of how the solar wind is formed, let's first look at the stratification of the solar atmosphere.
In general, the sun's atmosphere is divided into six layers, which are named from the inner one to the outer one: the core, the radiative zone, the convective zone, the photosphere, the chromosphere and the corona. The radius of the core accounts for about a quarter of the sun's radius, centralizing most of the sun's mass and producing more than 99 percent of the sun's energy. The photosphere is the brightest solar surface we can directly observe. All the visible light of the sun is emitted from the photosphere.
The corona is located in the outermost layer of the sun and belongs to the outer atmosphere of the sun, where the solar wind is formed and emitted. Images taken by satellites and space probes reveal long and large dark areas in the corona. The intensity of x-rays in these dark areas is much lower than that in other areas. These dark areas that look like holes in the corona are called coronal holes.
Coronal holes are the open areas of the sun's magnetic field, where the magnetic field lines spread into space and a large amount of plasma moves along the magnetic field lines, forming a high-speed flow of particles. Particles moving at the bottom of the coronal hole run at the speed of about 16 kilometers per second. When they come close to the earth's orbit, the speed can reach more than 800 kilometers per second. This kind of plasma with high speed movement is what we call solar wind.
After the eruption of solar wind from coronal holes, the sun's magnetic field carried by it will be blown around quickly. Solar wind has widespread effects, and it can blow through at least the entire solar system. When the solar wind travels around the earth, it is hitting the earth's magnetic field at the speed of about 400 kilometers per second.
When the solar wind reaches near the earth, it interacts with the dipole magnetic field of the earth, blowing the magnetic lines of force backwards in the earth magnetic field.
But the magnetic pressure of the earth's magnetic field blocks the flow of plasma, preventing the solar wind from invading the earth's atmosphere and continuing to move forward without going through the magnetic field. In this way, the cavities are formed with geomagnetic field contained inside and it looks like an egg with a bigger part on one side and a smaller part on the other side. However, when the sun experiences sudden and intense activity, the situation will change dramatically. At this point, the solar wind will have more high-energy ions, which can enter the earth's polar regions along the magnetic field line.
The magnetic field of earth is shaped like a funnel, with its tip pointing the north and south poles. Thus the charged particles from the sun can descend along the funnel and enter the earth's north and south poles. The upper atmosphere at the poles, under the bombardment of the solar wind, produces spectacular auroras which are called the aurora australis in the antarctic area and the aurora borealis in the arctic area. This kind of aurora is very beautiful.
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