Which atmospheric layer reflects and/or absorbs radio waves?

• A. Troposphere
• B. Stratosphere
• C. Ionosphere
• D. Mesosphere

Answer: (D)

Radio waves interact with parts of the atmosphere that are ionized, containing free electrons that can respond to the wave’s electric field. The layer that does this best is the ionosphere. It’s a region high above Earth where solar radiation strips electrons from atoms, creating a sea of charged particles. Those free electrons can oscillate with the radio wave and reflect it back toward the surface, or absorb energy at certain frequencies, allowing long-distance propagation of signals. Different sublayers (D, E, and F) have different effects: the D-layer tends to absorb lower-frequency waves during the day, while the E and F layers reflect higher-frequency waves, especially at night. Other atmospheric layers, like the troposphere, stratosphere, and the region where the mesosphere lies, don’t have enough ionization to reflect radio waves in the same way, so they don’t serve this reflecting/absorbing role.