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
Atmosphere of Earth takes place in the troposphere, and it is the only layer that can be accessed by propeller-driven aircraft. Within the five principal layers above, that are largely determined by temperature, several secondary layers may be distinguished by other properties: The average temperature of the atmosphere at Earth's surface is or , depending on the reference. The average atmospheric pressure at sea level is defined by the International Standard Atmosphere as . This is sometimes referred to as a unit of standard atmospheres (atm). Total atmospheric mass is 5.1480×10 kg (1.135×10 lb), about 2.5% less than would be inferred from the