layer

1. A tabular body of rock, ice, sediment, or soil lying parallel to the supporting surface and distinctly limited above and below. 2. One of several strata of ionized air, some of which exist only during the daytime, occurring at altitudes between 30 and 250 miles (50 and 400 kilometers); the layers reflect radio waves at certain frequencies and partially absorb others.

Related terms:

• D layer
• E layer
• F2 layer
• F layer
• boundary layer
• earth-layer propagation
• upper mixing layer
• F1 layer
• low-velocity layer
• oxygen minimum layer