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How do the F1 and F2 layers change between daytime and nighttime?

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Diagram of Earth's atmosphere layers-troposphere, stratosphere, mesosphere, and thermosphere-showing how temperature and air pressure change with increasing altitude, with key features like the ozone layer and pressure percentages at various heights. — Ionosphere and magnetosphere The layers of Earth's atmosphere, with a yellow line showing the air temperature at various heights.

In the F region of the ionosphere, the distinction between the F1 and F2 layers is primarily a daytime phenomenon.12

Daytime: The F region is characterized by two distinct layers. The F1 layer exists as a smaller, lower layer, while the F2 layer—also known as the Appleton layer—is situated above it as a more highly ionized, dominant layer.12
Nighttime: As the Sun sets, the ionization in the F1 region tends to disappear due to the recombination of electrons and ions into neutral gases. Consequently, the F1 and F2 layers merge into a single layer at approximately the altitude of the F2 layer.312

While the F1 layer effectively disappears at night, the F2 layer maintains a significant density of electrons. Ions produced at high altitudes during the day persist through the night and diffuse downward, which helps maintain the F2 peak and contributes to the effectiveness of shortwave radio propagation during nighttime hours.3