IZ4AKS

Aurora can affect propagation conditions over the polar routes and is often used to enhance VHF propagation, especially at 50 MHz and sometimes the 144 MHz Amateur bands. At times of auroral displays, HF radio signals traveling over the polar route will develop a distinctive warbling sound. You can often hear these effects on 14 MHz SSB signals that have followed the great circle route over the polar region.
During intense auroral activity, HF propagation down to the 3.5 MHz band can be affected. And if you are lucky enough to be in the right place, you can watch the spectacular visible auroral displays in the night-time sky (source hamradio-online.com).