How is long distance radio communication usually affected by the charged particles that reach Earth from solar coronal holes?
Why Coronal holes are gaps in the Sun's magnetic field that let high-speed solar wind streams escape. When those charged particles reach Earth they stir up the geomagnetic field, raising the A and K indices and triggering auroral absorption and ionospheric disturbance. The result is degraded or unstable HF propagation, especially on paths near the poles.
Watch out Improved HF conditions come from higher solar EUV/UV flux (high sunspot numbers and solar flux index), which ionizes the F layer without disturbing the magnetic field. VHF/UHF ducting is a tropospheric effect driven by weather and temperature inversions, not by solar particles.
Particles hurt, photons help: solar wind from coronal holes raises K index and kills HF.