D region

noun

the lowest region of the ionosphere (35 to 50 miles up) that reflects low-frequency radio waves

• Syn: ↑D-layer

• Instance Hypernyms: ↑region, ↑part

• Part Holonyms: ↑ionosphere

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noun

Usage: usually capitalized D

: the lowest part of the ionosphere occurring between 25 and 40 miles above the surface of the earth and capable of reflecting radio waves of very low frequency but absorbing energy of radio waves of high frequencies that are reflected by higher ionosphere layers

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the lowest region of the ionosphere, in which the D layer develops.

[1925-30]

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D region,

= D layer: (Cf. ↑D layer) »

The D region…is of great practical importance, since it contributes largely to the absorption of radio waves reflected from the ionosphere at any frequency, and determines the characteristics of waves on lower frequencies (New Scientist).