What influences all radiocommunication beyond ground wave or line-of-sight ranges?

Radiocommunication that travels beyond ground wave or direct line-of-sight depends on skywave propagation. Skywave propagation relies entirely on the Earth's ionosphere to refract radio signals back to the ground, and the state of the ionosphere is predominantly dictated by solar radiation. Ultraviolet and X-ray emissions from the sun strip electrons from atoms in the upper atmosphere, creating the ionized layers that refract radio waves. While specific layers like the F1 and F2 regions are important parts of this process, it is solar radiation as a whole that powers and creates all of these atmospheric changes. Lunar effects have no significant impact on radio propagation.