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D layer
D layern. The lowest region of the ionosphere, existing only during the day and extending from about 40 to 65 kilometers (25 to 40 miles) above the earth. Also called D region.D layer n. the lowest region of the ionosphere, at an altitude of ab. 50 mi. (80 km). [1930–35] D layer
D layer[′dē ‚lā·ər] (geology) The lower mantle of the earth, between a depth of 600 and 1800 miles (1000 and 2900 kilometers). (geophysics) 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. D layer A part of the ionosphere. It is a region of increasing electron and ion density, which exists primarily during the day. It merges with the bottom layers of the E layer. Its average height lies between 50 and 100 km (30 and 60 miles), and it reflects frequencies below about 50 kHz.ThesaurusSeeionosphere |