What's causing this? Protons accelerated by solar flares in the magnetic canopy of AR3664 are following the Parker Spiral back to Earth. Think of it as a magnetic superhighway. The arriving particles are funneled by our planet's magnetic field toward the poles where they ionize the atmosphere and interfere with the normal transmission of shortwave radio.
This polar cap absorption event could last for days, especially if it is boosted by more flares from AR3664. You can can monitor its progress here.
https://spaceweather.com/