I thought this was interesting:
The aurora borealis (northern lights) and aurora australis (southern lights) are created by the ionization of the E region of the ionosphere by streams of charged particles from the sun interacting with the Earth’s magnetic field.
The aurora does more than just make pretty lights in the sky; it can bend radio waves back to the earth as auroral propagation.
Since the aurora borealis occurs over northern Canada, two stations in the continental U.S. must each point their antennas to the north to use this mode.
With aurora there is a great deal of signal flutter. Phone tends to get garbled. CW is the most effective mode.
Click to hear CW auroral propagation.