Re: How and in what form does plasma exist in the atmosphere of Earth?

The two highest levels of the earth's atmosphere are plasma, or ionized gas. The lower level is called, appropriately, the ionosphere, and extends from an altitude of 70 km to about 1500 km. The atoms of gas in this region are heated by the sun's ultraviolet radiation and the solar wind. You can learn a bit about it at the SpaceWeb Textbook.

The upper region is known as the magnetosphere, and consists mostly of particles that are captured from the solar wind or evaporate from the ionosphere. I think the distinction between the ionosphere and the magnetosphere is that the particles in the ionosphere are still held to earth by the force of gravity, while particles in the magnetosphere are confined by the earth's magnetic field.

Hope this was helpful!

Jay