F1layer

F₁layer

[¦ef ′wən ‚lā·ər]

(geophysics)

The ionosphere layer beneath the F₂ layer during the day, at a virtual height of 120-180 miles (200-300 kilometers), being closest to earth around noon; characterized by a distinct maximum of free-electron density, except at high latitudes during winter, when the layer is not detectable.