Earth–ionosphere waveguide Earth–ionosphere waveguide The Earth–ionosphere waveguide refers to the phenomenon in which certain radio waves can propagate in the space between the ground and the boundary of the ionosphere. Because the ionosphere contains charged particles, it can behave as a conductor. The earth operates as a ground plane, and the resulting cavity behaves as a large waveguide. Extremely low frequency (ELF) (< 3 kHz) and very low frequency (VLF) (3–30 kHz) signals can propagate efficiently in this waveguide. For instance, lightning strikes launch a signal called radio atmospherics, which can travel many thousands of miles, because they are confined between the
Atmospheric diffraction Earth's surface. This phenomenon is sometimes called the corona effect, not to be confused with the solar corona. On the right is a 1/10-second exposure showing an overexposed full moon. The Moon is seen through thin vaporous clouds, which glow with a bright disk surrounded by an illuminated red ring. A longer exposure would show more faint colors beyond the outside red ring. Another form of atmospheric diffraction or bending of light occurs when light moves through fine layers of particulate dust trapped primarily in the middle layers of the troposphere. This effect differs from water based atmospheric diffraction because