06/06/2025
This graphic is scientifically/factually incorrect - here's the deal. When an x-ray flare erupts on the Earth-facing Sun (in other words, when in view of the Earth), it takes roughly eight minutes for the x-ray, extreme ultraviolet, radio, and light energy to reach Earth. The moment that energy reaches the ionosphere, it causes an increase in ionization of each layer of the ionosphere. The more the D-region is ionized, the greater and the higher in frequency the absorption of the radio wave energy. This effectively can shut down HF radio propagation (instantly, if the energy from the Sun is great enough - like a C-, M- or X-class flare) - this is the BLACKOUT and a blackout only occurs on the SUNLIT side of Earth. The higher ionospheric layers (E- and F-regions) enhance whatever radio waves make it THROUGH the D-region when not absorbed. This can cause interesting effects.
Now, if a coronal mass ejection is also triggered by that same flare, and IF that CME is directed toward Earth, it takes from one to four days for the CME to reach Earth. When it does, it interacts with the geomagnetic field. Depending on the magnetic orientation of the IMF (Interplanetary Magnetic Field) and the orientation of the plasma cloud of the CME, this interaction can cause geomagnetic fluctuations - sometimes very disturbed. We call this a SUBSTORM, or, a geomagnetic storm. These can cause the Maximum Usable Frequency (MUF) over a given radio path to become depressed by as much as roughly 40% over non-disturbed conditions. This graphic tries to merge the two phenomenon, getting timing and effects, incorrect.
So - solar flare - blackout. Then, recovery. Days later, the geomagnetic storm may occur if all the right things happen.
I am a propagation columnist - since 2001 - and have studied this topic since the 1970s.
