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How does the D region affect radio signals during the day?

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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.

During the day, the D region of the ionosphere significantly impacts radio transmissions by acting as an absorbing layer rather than a reflector.

While the D region can provide some reflection, its primary effect during daylight hours is the absorption of medium frequencies and the lower frequencies of the shortwave bands. Because it attenuates these radio waves, it limits the range of radio transmissions during the day, causing a marked reduction in their reach compared to nighttime conditions.123

This interference occurs because the D region exists only during daylight hours, when solar energy causes the ionization of atmospheric gases. At night, the free electrons in this region recombine with ions to form neutral gases, causing the layer to effectively disappear and allowing radio waves to pass through to the more strongly reflecting E and F layers above.2314