A polar aurora is a luminous phenomenon produced when particles in the solar wind collide with particles in the Earth's atmosphere, more specifically those in the thermosphere.
In the course of the nuclear reactions taking place in the Sun, a huge amount of energy is released, resulting in nuclear particles. This flow of matter released by the Sun, in the form of small particles, forms what is called the solar wind.
If solar wind particles were to reach the Earth’s surface, they would prevent all or almost all life on Earth. Indeed, all living organisms would be constantly exposed to these particles, and this could affect their integrity given the radioactivity of the solar wind. Fortunately, the Earth has a shield against the solar wind: the magnetosphere.
The magnetosphere is a huge magnetic field that surrounds Earth in a non-circular pattern.
It is generated by the motions of the liquid metallic core of the Earth’s deep layers. The Earth's core therefore resembles a huge magnet that produces a magnetic field around the Earth. This magnetic field moves from the north magnetic pole to the south magnetic pole.
The Earth's magnetic field plays a vital role in the development of life on Earth by deflecting deadly solar wind particles. When the core will have cooled and solidified (in a few billion years) and the magnetic field will have disappeared, it is likely that existing life forms will no longer be able to survive. Normally, the magnetosphere absorbs all solar wind particles without causing any particular phenomenon. However, when solar activity is intense, the amount of particles released may be too large for the capacity of the magnetosphere, which causes the formation of polar auroras.
It is worth noting that the magnetic and geographic poles are reversed. In fact, we find near the north geographic pole (Ng) the south magnetic pole (Sm). In fact, the Earth's north pole is a south magnetic pole that attracts the north point of a compass, the red needle.
Usually, the magnetosphere absorbs all the solar wind particles without causing any particular phenomenon. However, when solar activity is intense, the amount of particles released may be too large for the capacity of the magnetosphere. In this case, it spills its overflow into the atmosphere near the poles. The particles of the solar wind then collide with the gases present in the thermosphere. This interaction results in the production of light, thus making the polar aurora visible.
The luminous phenomenon of the polar aurora is called aurora borealis when it is seen at the north pole and aurora australis when it occurs at the south pole of the Earth.
The aurora borealis occur in the thermosphere, one of the highest layers of the atmosphere. Depending on the altitude at which the phenomenon occurs, the colours emitted will vary between red, yellow, green, purple, and blue. The colour difference of the polar auroras is due to the type of gas ionized by solar winds.
At altitudes of 100 to 200 km, the colours produced may be yellow, green, or pink when oxygen |(O_2)| is present. They may be blue, purple, or red when nitrogen |(N_2)| is present.