Radio waves interact with the atmosphere in ways that affect how they travel, mainly through reflection and refraction:
Reflection:
- Radio waves can bounce off certain atmospheric layers or surfaces, changing their direction.
- The most important reflector is the ionosphere, a charged layer of the upper atmosphere. It can reflect lower-frequency radio waves (like shortwaves), enabling them to travel beyond the horizon and reach distant locations.
- Radio waves can also reflect off the Earth’s surface, buildings, or bodies of water, sometimes causing echoes or multipath interference.
Refraction:
- Refraction occurs when radio waves bend as they pass through layers of the atmosphere with different densities or temperatures.
- The atmosphere’s density decreases with altitude, causing radio waves to gradually bend downward, slightly extending their range beyond the visual horizon.
- Changes in atmospheric conditions, such as temperature inversions, can increase this bending effect, leading to phenomena like tropospheric ducting, which allows signals to travel unusually far.