We had an M8.4 solar today, commencing at 1715 UTC, and ending at, well, it still seems to be going on, the x-ray flux level is still C3 at 2300 UTC.
The effects were rather dramatic, for those of us on the sunlit side of the Earth. First, here’s a graph of the x-ray intensities of the flare itself, as measured by the GOES-15 weather satellite (in geosynchronous orbit around the Earth):
The effects were dramatic, virtually all of HF was completely silent here, just static. The intense x-rays from the flare caused strong ionization of the D layer of the ionosphere. The D layer absorbs radio waves, it does not reflect them like the E and F layers that we rely on for shortwave propagation.
Here’s a graph showing the absorption at HF radio frequencies caused by the flare, as displayed by DX ToolBox:
You can view the signal strengths for various frequencies as recorded by my dedicated SDR setup here: http://www.hfunderground.com/propagation Take a look at various stations such as CFRX 6070 kHz and CHU 7850 kHz, and see how they completely faded out during the flare. They also are not present at night, which is normal.