Which term describes the phenomenon when signals reflect off the ionosphere?

The term that describes the phenomenon when signals reflect off the ionosphere is "skip." This occurs when radio waves, especially those in the HF (High Frequency) band, travel upward into the ionosphere where they encounter layers of ionized particles. Instead of continuing into space, some of these waves are reflected back toward the Earth. This reflection allows communications to take place over long distances, beyond the line of sight.

Understanding skip is crucial for amateur radio operators as it can greatly influence the propagation of signals, particularly during different times of the day and solar cycle phases. The amount of ionization in the ionosphere varies, which affects how well signals are refracted or reflected back to Earth.

Refracting refers to the bending of waves as they pass through different media, which isn’t the primary mechanism at play with ionospheric signals. Diffraction involves the bending of waves around obstacles or through openings but does not specifically relate to the ionospheric reflection phenomena. While reflection could be considered a general description of the process, skip is the specific term used in the context of radio communication involving the ionosphere.