Which of these emission modes is best for auroral propagation?

Signals reflected via auroral propagation undergo extreme distortion. The auroral curtain is highly dynamic and constantly moving, which introduces rapid multipath fading and severe Doppler spread. This gives reflected signals a characteristic raspy, hissing sound. Because of this intense distortion, voice modes like SSB and FM become completely unintelligible. The phase and frequency modulation characteristics are destroyed by the rapid fluttering of the aurora. CW (Continuous Wave) is the most effective mode for this propagation because it relies solely on the presence or absence of the carrier. Even when the signal sounds like a burst of static, an operator can still interpret the on/off timing of the Morse code.