Space weather

Aurora Propagation: When the Magnetic Field Becomes a Reflector

Aurora propagation is a VHF and UHF mode that uses ionized auroral curtains as reflectors. During strong geomagnetic storms, energetic particles from the sun excite atmospheric atoms over the polar regions, producing visible aurora and a vertical sheet of ionization that can scatter radio signals back to earth. Aurora is most useful on 6 meters, 10 meters, and 2 meters; signals are characterized by a distinctive narrowband “rasp” caused by Doppler spread from the moving auroral structures.

Why it matters for HF operating

For most HF operators, aurora is a problem rather than an opportunity: it absorbs HF signals on high-latitude paths and contributes to band closures during storms. But for operators willing to point antennas at the magnetic pole during storms, aurora can deliver contacts on 6 meters and 10 meters that are not possible by any other mode. Distances of 800 to 2000 km are typical, and the band rotates with the auroral oval throughout the storm.

Key values to know

  • Trigger. Kp of 5 or higher and the auroral oval expanding into mid latitudes.
  • Frequency range. 28 MHz, 50 MHz, and 144 MHz are the most active. Aurora rarely supports 432 MHz.
  • Antenna pointing. Beams point toward the auroral oval (north for North America, south for the southern hemisphere) regardless of where the target station is geographically.
  • Signal character. Distinctive “rasp” or “ssb sounds like cw at high speed.” CW is preferred because SSB voice is often unintelligible.
  • Latitude window. Most useful for operators between 35 and 60 degrees latitude.

Common misconceptions

Aurora is not a typical HF propagation mode. It is a VHF and UHF phenomenon that lives at the edge of the HF spectrum (10 meters can sometimes work). HF operators who hear aurora effects on 20 meters or 17 meters are usually hearing other geomagnetic-storm side effects (D-layer absorption, F2 collapse), not aurora reflection. Confusing the two leads to expecting aurora to “open” the lower bands during storms, when the lower bands are typically just degraded.

SkyWave shows Kp and storm state on the Go screen, so you know when aurora propagation is worth investigating on the higher bands. See it in the app →