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How do solar X-rays change Earth’s ionosphere?

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Space weather Earth's full North Polar auroral oval, in an image taken in ultraviolet light by the U.S. Polar spacecraft over northern Canada, April 6, 1996. In the colour-coded image, which simultaneously shows dayside and nightside auroral activity, the most intense levels of activity are red, and the lowest levels are blue. Polar, launched in February 1996, was designed to further scientists' understanding of how plasma energy contained in the solar wind interacts with Earth's magnetosphere.

Solar X-rays play a fundamental role in the structure and function of Earth’s ionosphere. The soft (long-wavelength) X-rays emitted from the solar corona are responsible for producing the specific ionospheric layers that enable shortwave radio communication.1

The impact of these X-rays changes based on solar activity:

Increased Solar Activity: As solar activity rises, soft X-ray emissions increase. While this initially creates a more effective reflecting layer for radio waves, excessive increases in ionospheric density can eventually lead to the absorption of radio signals, hampering communications.1
Solar Flares: Harder (shorter-wavelength) X-ray pulses from solar flares ionize the lowest region of the ionosphere, known as the D-layer. This process can cause radio fade-outs, where signals are absorbed rather than reflected.1

Because the ionosphere acts as a medium for radio wave propagation, these X-ray-induced density changes can significantly affect satellite communications and GPS accuracy by causing signals to be bent, absorbed, or reflected.2