[F2 layer] n (1933): the upper of the two layers into which the F region of the ionosphere splits in the daytime at varying heights from about 120 miles (200 kilometers) to more than 300 miles (500 kilometers) above the earth
F2 LAYER
Meaning of F2 LAYER in English
Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012