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1. The highest region of the ionosphere, extending at night from about 190 to 400 kilometers (120 to 250 miles) and during the day from about 145 to 400 kilometers (90 to 250 miles) above the earth. Also called F region.
2. Either of two layers, designated F1 and F2, into which this region is divided during the day, extending respectively from about 145 to 240 kilometers (90 to 150 miles) and from about 190 to 400 kilometers (120 to 250 miles) above the earth.
the highest radio-reflective region of the ionosphere, at an altitude of ab. 80 mi. (130 km).
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|Noun||1.||F layer - the highest region of the ionosphere (from 90 to 600 miles up) which contains the highest concentration of free electrons and is most useful for long-range radio transmission|
ionosphere - the outer region of the Earth's atmosphere; contains a high concentration of free electrons