Earth Magnetosphere and Upper atmosphere


When an atom or a molecule collides with another particle, it can gain internal energy which will be lost by the emission of light. This is the main mechanism responsible for both the daytime airglow and the polar aurorae. When the ultraviolet radiation of the Sun is absorbed by gases in the upper atmosphere, these gases ionize and produce electrons which subsequently collide with the constituents of the upper atmosphere. This interaction results in light emission: the dayglow.

On the other hand, the Earth's magnetic field interacts with the solar wind, a continuous flow of charged particles emitted by the Sun in which the solar magnetic field is frozen. The energy exchanged during this interaction stimulates the precipitation of charged particles from the magnetosphere into the upper atmosphere. These particles collide with the gas constituents of the upper atmosphere, causing their ionization. Secondary electrons, produced in large number by that process, collide in turn with the surrounding gas, causing light emission called the polar aurora. Hence, the same physical mechanisms are at work in the dayglow and aurorae. However, other mechanisms can also lead to the emission of light by gases in the upper atmosphere: the products of some chemical reactions (atoms, molecules or even ions) have an excess of energy that will be released in the form of light emission. This type of mechanism is important in the nightside upper atmosphere of the Earth, and produce the nightglow. These phenomena are also important in the atmosphere of comets, also called the coma. Some of these radiations emitted by the coma are produced by mechanisms physically comparable to those at work in planetary atmospheres. As far as we know, the laws of physics are the same everywhere in the Universe depending on the prevailing conditions, which makes it possible to understand how it works...

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