d region

noun

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

noun

1. the lowest region of the ionosphere, extending from a height of about 60 kilometres to about 90 kilometres: contains a low concentration of free electrons and reflects low-frequency radio wavesSee also ionosphere

1. The region of the atmosphere that lies in the upper mesosphere, extending from about 70 to 90 km (43 to 56 mi) above the Earth. The D region is responsible for the daytime absorption of high-frequency radio signals; at night, oxygen ions recombine with free electrons and form oxygen molecules that are transparent to such signals, which bounce off of the E region and back to Earth. Also called D layer Compare E region F region.