What is the cause of short-term radio blackouts?

Short-term radio blackouts are primarily caused by solar flares, which are sudden eruptions of intense high-energy electromagnetic radiation (like X-rays and ultraviolet light) from the Sun. Traveling at the speed of light, this radiation hits Earth in about 8 minutes. When this intense radiation reaches the Earth's ionosphere, it significantly increases the ionization in the D-region on the sunlit side of the planet. This highly ionized D-layer acts like a sponge, quickly absorbing HF radio waves rather than letting them pass through to the higher refracting layers. Coronal mass ejections (CMEs), on the other hand, are ejections of physical particles that take days to reach Earth, causing longer-term geomagnetic storms rather than immediate, short-term blackouts.