Thermosphere: The Ionosphere
The thermosphere is a layer of Earth's atmosphere located between the mesosphere and exosphere, approximately 80 km to 550 km above the Earth's surface. It is known for its extremely high temperatures due to the absorption of solar radiation.

The Ionosphere
The thermosphere is also known as the ionosphere because it is filled with ions and free electrons that are created by the ionization of various molecules and atoms through the absorption of high-energy solar radiation. These ions and free electrons play a crucial role in the propagation of radio waves as they reflect and refract radio signals back to Earth, enabling long-distance communication.

Ionization Process
The ionization process in the ionosphere occurs when solar radiation strips electrons from neutral atoms and molecules, creating positively charged ions and free electrons. This process is more pronounced in the thermosphere due to the high energy levels of solar radiation in this region of the atmosphere.

Effects on Communication
The presence of ions and free electrons in the ionosphere affects radio wave propagation. Different frequencies of radio waves interact with the ionosphere in various ways, allowing for long-distance communication by reflecting signals off the ionosphere back to Earth. This phenomenon is essential for activities such as global communication, navigation systems, and radio broadcasting.

Conclusion
In summary, the thermosphere is known as the ionosphere due to the abundance of ions and free electrons created by the ionization process in this region of the atmosphere. This ionization plays a vital role in facilitating long-distance communication through the reflection and refraction of radio waves.