The E layer, also known as the E region, is a part of the Earth's ionosphere, located approximately 90 to 150 kilometers above the surface. It plays a crucial role in radio wave propagation, as it reflects certain frequencies back to the Earth, allowing for long-distance communication. The E layer is formed by the ionization of atmospheric gases due to solar radiation. This layer is most active during the daytime when solar energy is at its peak. Its characteristics can change with the time of day, season, and solar activity, influencing the performance of radio communications and navigation systems.