"Aurora", also known as Aurora Borealis (or Northern Lights), is often used by radio amateurs to enhance propagation on VHF (or sometimes UHF) bands. The most common bands used to take advantage of Aurora propagation is 50 and 144 MHz. CW (Morse code) radio signals when reflected from the auroral curtain normally sound raspy. Phone (voice) signals that are reflected also sound raspy, whisper-like, watery, and sometimes very difficult to understand (especially at higher frequencies). Phone can be used at 50 or 144 MHz but becomes extremely difficult or in some cases impossible to understand above those frequencies so CW is normally used instead.

Recordings of a phone (voice) signals enhanced by auroral propagation on 50 MHz:

VE6NTT from Calgary (one of the strongest aurora signals I've ever heard)

unknown station from Washington State (typical auroral signal)

K7WIA from Seattle, Washington (typical auroral signal)

Other auroral recordings of the VE6EMU 50 MHz beacon:

   Recording #2

   Recording #3

"Auroral-E" is also another propagation mode used on the VHF bands. Instead of bouncing the radio signals off the auroral curtain as aurora signals do, "auroral-E" uses more of a direct path (Great Circle Path) but still bounces off ionization patches left behind by aurora conditions. Radio signals sound somewhat 'normal' and intelligible but still often have a hollow or fluttering sound to them. 

Here's an Auroral-E recording also on 50 MHz:

  KL7NO from Fairbanks, Alaska