On a double-hop path involving the surface of the Earth as a middle point, what phenomenon returns the radio wave to the ionosphere?

In multi-hop propagation, a radio wave alternates between bending in the ionosphere and bouncing off the surface of the Earth. When the wave hits the Earth's surface—especially highly conductive surfaces like saltwater—it bounces back upward. This specific bouncing action is called reflection. It is important to distinguish this from what happens in the sky. In the ionosphere, the wave doesn't bounce off a hard surface; instead, it gradually bends as it travels through ionized gases. That bending process is called refraction. Diffraction refers to waves bending around solid obstacles (like mountains), and scattering occurs when signals disperse randomly in multiple directions. For a reliable double-hop path, the Earth acts as a mirror, creating a true reflection.