Meaning of F layer

F layer

Pronunciation: [key]
— Physics. Physics.
  1. the highest of the radio-reflective ionospheric layers, beginning at an altitude of ab. 80 mi. (130 km) and consisting of two parts, the lower partbeing detectable in the daytime only, the higherbeing constant and constituting the ionospheric layer most favorable for long-range radio communication.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.