Which analog emission mode is the most reliable in auroral propagation?

Auroral propagation severely distorts radio signals by scattering them off a rapidly moving, highly ionized curtain of particles. This rapid movement introduces extreme multipath fading and Doppler shift, creating a phenomenon known as 'auroral flutter'. Continuous Wave (CW, or Morse code) remains the most reliable analog mode under these harsh conditions. Because CW relies simply on turning a carrier wave on and off, a receiving operator can still recognize the rhythm of the signal even if the tone itself sounds like a raspy, distorted hiss. Voice modes like FM or SSB quickly become completely unintelligible due to the intense flutter and distortion.