Why Auroral propagation works by scattering VHF signals off the rapidly shifting, highly ionized curtains of an aurora. Because the ionization is in constant, turbulent motion, each reflection gets a slightly different Doppler shift, smearing the signal in frequency. The result is a buzzy, raspy, distorted sound that makes SSB hard to copy, which is why CW is the preferred mode for auroral work.
Watch out The idea that signals are strongest with the antenna pointed west is a trap: in the northern hemisphere you aim north toward the auroral zone, not at the station you are working. Distances of 10,000 miles describe long-path HF skip, not VHF aurora, and auroras follow geomagnetic storms rather than a winter-nighttime-only schedule.
Aurora = raspy. Point north, send CW, expect a buzz.