Explanation:
The ionosphere is the uppermost layer of the Earth's atmosphere, located between the mesosphere and the exosphere. It is called the ionosphere because it is ionized by solar radiation. The ionosphere is responsible for radio communication as it reflects radio waves back to the earth's surface.

The temperature in the ionosphere increases rapidly due to the absorption of high-energy solar radiation, especially in the form of ultraviolet and X-rays. This is because the ionosphere is composed of charged particles, such as ions and free electrons, which are easily excited by high-energy radiation. The energy absorbed by these particles causes them to vibrate more rapidly, which increases the temperature of the ionosphere.

The temperature increase in the ionosphere is not uniform and varies with altitude. At lower altitudes, the temperature increase is more significant due to the higher density of charged particles, while at higher altitudes, the temperature increase is less pronounced due to the lower density of particles.

In summary, the temperature increases rapidly in the ionosphere due to the absorption of high-energy solar radiation by charged particles, leading to their increased vibration and a rise in temperature.