Aurora and Radio
The same storm that lights up the prairie sky can wipe out a polar path on 20 m, put a buzz on 6 m CW and open 2 m to stations you’d never normally hear. Here’s what’s going on, and how to use it.
When a burst from the sun hits Earth’s magnetic field, the effects reach well beyond the light show. Charged particles pour into the upper atmosphere around the magnetic poles. They add extra ionization in the E and D regions, and they stir up the F region that HF depends on.
For HF that usually means trouble; for VHF it can mean opportunity. Most of the change happens in and near the auroral oval, the ring of activity around the magnetic pole that grows and moves south during a storm.
Usually worse
Absorption, fading and flutter, worst on polar paths. Some north-south paths hold up, and there is the odd short-lived boost.
Aurora scatter
Point north, and signals bounce off the aurora with a rough, buzzing note. CW works best.
Auroral E
Cleaner E-layer openings, often after the aurora scatter fades and often after midnight. These can reach thousands of kilometres.
What a storm does to HF
Absorption
Particles raining into the lower ionosphere add ionization to the D region. That layer doesn’t reflect HF. It soaks it up, and the lower the frequency, the worse the loss. Under the auroral oval this auroral absorption can make the low bands go quiet.
A separate effect, polar cap absorption (PCA), comes from high-energy solar protons. It can black out HF across the polar cap for hours or even days. PCA and geomagnetic storms often arrive around the same time, but they are different events.
Why polar paths suffer most
From southern Alberta, the short path to Europe heads northeast over Hudson Bay and Greenland. The path to Japan heads northwest over Alaska and the Aleutians. Both run through or close to the auroral zone, so during a storm those paths may weaken or close completely.
Paths that stay further south, toward South America, the South Pacific and Australia, often keep working when the polar routes are dead.
Auroral flutter
A signal that passes through the disturbed auroral ionosphere picks up rapid, watery fading. Hams call it auroral flutter. SSB sounds as if the speaker is talking through a fan, and CW gets a fuzzy edge.
Can a storm ever help?
Sometimes, for a short while. Early in some storms the F region briefly gets denser, and MUFs can rise for a few hours (the “positive phase”). This is often followed by a longer “negative phase,” when MUFs drop below normal and the upper bands go flat. That can last a day or more.
The biggest gift, though, is on VHF, through aurora scatter and auroral E.
NOAA’s own summary. On NOAA’s G scale, a G2 storm brings HF fading at higher latitudes, G3 brings intermittent HF, G4 makes HF sporadic, and in a G5 storm HF may be impossible in many areas for one to two days.
VHF aurora scatter on 6 m and 2 m
During a good storm the aurora itself becomes a radio reflector. The scattering happens in clouds of ionization at E-region heights, about 100 to 150 km up. You don’t need to see the aurora. Radio aurora can turn up in daylight too.
The sound
The aurora is moving, so the signals come back smeared in frequency by Doppler shift. On 2 m the spread is roughly half a kilohertz. The result is a rough, rasping, hissing or buzzing note that sounds nothing like a normal signal.
CW turns into a raspy hiss, and SSB sounds like a hoarse whisper. On 6 m the distortion is usually milder than on 2 m, and SSB is often readable. FM is generally not worth trying.
Why CW works best
CW takes up so little bandwidth that it’s still readable when the spreading ruins voice. That’s why the Canadian Basic qualification question bank says it: CW is the most reliable analog mode in aurora, “because it is readable even when distorted.” Send a little slower than normal.
In reports, the tone figure of RST is replaced by an A for aurora, so a typical report is 57A.
Beam north, then hunt
- Start with the antenna pointed north, toward the aurora, not toward the station you want to work. Signals reach you by bouncing off the aurora.
- Swing the beam slowly either side of north to find the peak. The best heading moves as the aurora shifts, so keep checking.
- Tune around a little. Aurora signals can sit slightly off the expected frequency.
- Horizontal or vertical polarization doesn’t matter much.
When to listen
Aurora scatter often starts in the late afternoon or evening when the field is disturbed, and it can come back late in the evening and after midnight. It comes and goes, so if it stops, keep listening. It can return within half an hour.
Openings are most common around the equinoxes. Radio aurora also tends to peak a year or two after sunspot maximum. Solar Cycle 25 peaked in October 2024, so the next while could be a good time to try.
How far?
On 2 m, north-south aurora contacts top out around 1,000 km, and east-west paths can reach around 2,000 km. Six metres goes further.
The Pacific Northwest VHF Society lists regional distance records of more than 4,000 km by aurora on 50 MHz. One of them is from a British Columbia station near 50° N to Maine. On 144 MHz its listed aurora record is 1,775 km.
Auroral E (Au-E)
Auroral E is E-layer propagation tied to the aurora. Hams use the name a little loosely, but the pattern is the same: it often appears once the buzzy aurora scatter fades, and on 6 m it is usually after midnight.
The signals are much cleaner than aurora scatter, with little or none of the rasp. Because it is a forward path, you point the beam at the other station, not at the aurora.
Distances can be large. On 6 m, auroral E can stretch to about 4,000 km across the northern states and Canada. On 2 m it’s rare, but the Pacific Northwest VHF Society lists a 2,446 km auroral E contact as a North American record.
Tip: after an aurora session on 6 m, don’t shut down. Check for clean signals from the east or west in the small hours. That’s often how auroral E shows itself.
Reading the space weather numbers
| Number | What it tells you | What to watch for |
|---|---|---|
| Kp | How disturbed Earth’s magnetic field is, on a 0 to 9 scale over three-hour blocks. | Kp 5 or higher is a storm. Kp 4 to 5 and up is worth a listen on 6 m from here. |
| G scale | NOAA’s storm level: G1 is Kp 5, G2 is Kp 6, G3 is Kp 7, G4 is Kp 8 to 9-, and G5 is Kp 9. | G2 and above: expect HF trouble at high latitudes and a better shot at VHF aurora. |
| Bz | The north-south direction of the magnetic field carried by the solar wind. | Southward (negative) Bz lets energy into Earth’s field. The longer and stronger it stays south, the bigger the storm. |
| Solar wind speed | How fast the solar wind is hitting us. | A sudden jump means a shock or a fast stream has arrived. Fast wind plus southward Bz is the recipe for aurora. |
| Density | How many particles are in the wind. | A spike along with the speed jump often marks a CME arriving. |
Solar wind data come from spacecraft upstream of Earth, giving roughly 30 to 90 minutes’ warning. Kp is a planet-wide average, so local conditions can differ.
Which bands to try
| When | Try | Why |
|---|---|---|
| Storm building (Bz south, Kp rising) | 6 m CW and SSB, beam north. 2 m CW if Kp keeps climbing. | Aurora scatter |
| During the storm, daytime | 15 m to 20 m on north-south paths. Check the upper bands for a short positive-phase lift. | Polar paths are absorbed, and lower latitude paths hold up better |
| During the storm, night | 40 m and 80 m to the south. Expect the low bands to be noisy or absorbed on northern paths. | Auroral absorption is strongest under the oval |
| After midnight, as the aurora fades | 6 m, beam toward the stations you hear | Auroral E |
| One to three days after | Lower than usual. Use our MUF and band tools. | The negative phase depresses MUF, then it recovers |
The local angle: Lethbridge and aurora
Lethbridge is at about 49.7° N on the map, but about 56 to 57° in geomagnetic terms. Geomagnetically, that’s about level with northern England, where 2 m and 6 m aurora are long-established modes. It’s also a little north of southern British Columbia, where 6 m aurora and auroral E contacts of more than 4,000 km are on record.
So on good storm nights, aurora scatter should be workable from here, especially on 6 m. On 2 m it may be possible during stronger storms.
Being honest about it. We haven’t found published aurora contacts from Lethbridge itself, so treat this as a well-grounded expectation, not a guarantee. Quiet or minor storms (Kp 4 to 5) may give nothing here. G2 and stronger storms are the realistic targets. If you work aurora from southern Alberta, log it. That’s useful data.
Safety and etiquette
Safety
- Storms often bring cold, clear, windy nights. Don’t climb towers or touch rotators in ice or wind just to chase an opening.
- VHF beams and amplifiers can put out a lot of RF. Follow Canadian RF exposure limits, and keep people and pets clear of the antenna while you transmit.
- Operating portable from a dark hill? Park well off the road, wear something reflective and tell someone where you are.
Etiquette
- Listen first. Aurora signals are weak and smeared, so a minute of listening saves a lot of calling over people.
- Keep contacts short: calls, report with an A, grid square, done.
- Use the CW and weak-signal segments, and don’t sit on the SSB calling frequencies (50.125 and 144.200 MHz). Make contact, then move.
- Spot openings on the cluster with “AU” or “Au-E” so others know.
Want to see it, not just hear it? For viewing tips, photo tips and where to watch near Lethbridge, see Northern Lights over Lethbridge. For live numbers, check the live aurora predictor and live storm status on PropMap.