Propagation
Radio propagation
Current solar-terrestrial propagation conditions for HF and VHF – from two sources for comparison.
Whether a long-distance HF contact succeeds depends heavily on solar activity. The solar flux index (SFI), the A and K indices and the state of the ionosphere determine which bands are open. On the left the well-known overview from hamqsl.com, on the right the primary data from the US space weather service NOAA SWPC.
hamqsl.com (N0NBH)
NOAA SWPC (primary data)
Loading data …
| Index | Current | As of (UTC) |
|---|---|---|
| SFI | – | |
| Sunspots SSN | – | |
| A index (planetary, daily) | – | |
| Kp index (3 h) | – | |
| X-ray flux (GOES) | – | |
| Solar wind | – | |
| Bz / Bt | – | |
| NOAA scales | – |
Kp: last 24 h and forecast
observed estimated forecast · vertical bar = now · red line = Kp 5 (storm)
Outlook
| Day (UTC) | SFI | Ap | Kp max | G |
|---|
Source: NOAA Space Weather Prediction Center ↗, fetched every 10 minutes via our server (no visitor data is sent to NOAA). Fetched: –
Aurora forecast
NOAA's OVATION model shows where aurora is likely within the next 30 to 90 minutes. A large auroral oval means disturbed HF paths across the polar regions – and sometimes aurora contacts on 6 m and 2 m.
Why do the values differ?
- Timing: The SFI is measured several times a day in Penticton (Canada), sunspot numbers and the A index are daily values, and each Kp value covers three hours. Depending on when a source last updated, different values are shown.
- Method: Sunspot numbers are determined differently by different organisations (e.g. NOAA/SESC or SILSO in Brussels) and often differ considerably. K and A indices exist both regionally (e.g. Boulder) and planetary.
- Forecast or measurement: Outlook values are predictions and can differ greatly from what is later measured.
What matters is always the time stamp next to the value.