D layer

1. The lower mantle of the earth, between a depth of 600 and 1800 miles (1000 and 2900 kilometers). 2. The lowest layer of ionized air above the earth, occurring in the D region only in the daytime hemisphere; reflects frequencies below about 50 kilohertz and partially absorbs higher-frequency waves.

Related terms:

• layer
• F layer
• E layer
• F2 layer
• upper mixing layer
• earth-layer propagation
• F1 layer
• sporadic E layer
• boundary layer
• isothermal layer