Atmospheric diffraction regularly with a 6 watt transmitter from the middle of the Pacific. For more details see the "communications" part of the "Kon-Tiki expedition" entry in Wikipedia. An exotic variant of this radio wave propagation has been examined to show that, theoretically, the ionospheric bounce could be greatly exaggerated if a high powered spherical acoustical wave were created in the ionosphere from a source on earth. In the case of sound waves travelling near the Earth's surface, the waves are diffracted or bent as they traverse by a geometric edge, such as a wall or building. This phenomenon leads to a
Radio propagation propagation. The interference between the direct beam line-of-sight and the ground reflected beam often leads to an effective inverse-fourth-power (1/distance) law for ground-plane limited radiation. Lower frequency (between 30 and 3,000 kHz) vertically polarized radio waves can travel as surface waves following the contour of the Earth; this is called "groundwave" propagation. In this mode the radio wave propagates by interacting with the conductive surface of the Earth. The wave "clings" to the surface and thus follows the curvature of the Earth, so groundwaves can travel over mountains and beyond the horizon. Ground waves propagate in vertical polarization so vertical