F₁ layer

atmospheric science

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June 26, 2026

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The F1 layer is the lower of two layers within the F region of the ionosphere, typically found between 80 and 120 miles (130 to 200 kilometers) above Earth's surface. This region is the highest part of the ionosphere, with altitudes greater than 160 km (100 miles), and contains the highest concentration of free electrons. During the day, the F region often splits into the F1 layer and a more ionized F2 layer above it. At night, these layers merge into a single layer known as the Appleton layer. The F region, including the F1 layer, plays a crucial role in reflecting radio waves, with frequencies up to approximately 35 megahertz being reflected.123

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ionosphere and magnetosphere
F region
…a small layer known as F₁ and above it a more highly ionized dominant layer called F₂. At night they merge at about the level of the F₂ layer, which is also called the Appleton layer. This region reflects radio waves with frequencies up to about 35 megahertz; the exact…
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…a small layer known as F₁ and above it a more highly ionized dominant layer called F₂. At night they merge at about the level of the F₂ layer, which is also called the Appleton layer. This region reflects radio waves with frequencies up to about 35 megahertz; the exact…
Read More