Roelof -  I can confirm its like adding a 50dB attenuator to HF and long range MF/LF signals here. Very fast onset and slooooooooowwwwwer recovery- thats typically from just outside of the Auroral Oval (depending on how South its moved) but inside the Oval  say at 83N its like being in a partially mirrored fish bowl with a large diode effect. You can often still hear DX MF and LF signals at very very low levels but (mostly) the noise levels are really low - so low Ive taken front ends apart to find the problem.
 
Laurence KL7 L