Auroras occur in the thermosphere and ionosphere regions of the Earth's atmosphere. The thermosphere is the uppermost layer of the atmosphere, extending from about 80 kilometers (50 miles) above the Earth's surface to the edge of space. It is a region with very low density and high temperatures.
The ionosphere, on the other hand, is a layer within the thermosphere where the Sun's ultraviolet (UV) radiation ionizes the gas molecules, creating ions and free electrons. This ionization process is responsible for the auroras.
Auroras, also known as the Northern Lights (Aurora Borealis) and Southern Lights (Aurora Australis), are caused by interactions between charged particles from the Sun, called solar wind, and the Earth's magnetic field. When the solar wind particles reach the Earth's magnetosphere, they are funneled towards the polar regions, where the magnetic field is stronger. As these charged particles collide with atoms and molecules in the thermosphere and ionosphere, they emit light, resulting in the beautiful and colorful displays known as auroras.
Therefore, auroras occur in the thermosphere and ionosphere due to the interaction between the solar wind particles and the Earth's magnetic field in those atmospheric regions.