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Propagation News – 5 September 2021

Well, NOAA got the solar flux index prediction wrong last week. The SFI actually ended up higher than the prediction, thanks to active region 2860, which grew as the week went on. NOAA also issued a G1, or Minor, and G2, or Moderate, geomagnetic storm watch for the 1st and 2nd of September, just days after two CMEs occurred on the 28th of August. The first was associated with an M4 X-ray flare, or R1-Minor Radio Blackout. The second CME was associated with a filament eruption. As of 1800 on Thursday it looks like this may have been over cautious as no disturbance had occurred. Active region 2863 has now rotated into view, but on Thursday it still looked quite small and non-threatening.

There are signs of HF propagation improving as we move to more autumnal ionospheric conditions. Antoine, 3D2AG and Dominik, 3D2USU in Fiji were both logged on 17 metres this week and ZS1OIN in South Africa was noted on 15 metres. Chris, G3SJJ reports working Chile on 15 and 20 metres, along with Uruguay, Peru and Puerto Rico on 20m.

The equinoxes are typically very good for North-South paths so we can expect conditions to improve as the month wears on. Propquest shows that the maximum usable frequency over a 3,000km path is generally struggling to reach 18MHz during the day.

Next week NOAA predicts the SFI will decline into the low 80s, due to a lack of serious sunspot activity. It also predicts a maximum Kp index of two. However, a large equatorial coronal hole was Earth-facing on Thursday, so we may expect a geomagnetic disturbance and higher Kp index across this weekend, due to the incoming plasma from the high-speed solar wind.

VHF and up propagation news:

The prolonged spell of high pressure weather has produced some strong lift conditions across the country and surrounding seas. Unfortunately, it seems the high will probably suffer some knocks during the coming week and there will be some rain or showers. However, there is a good chance the high will fight back, to some extent, and there may be further Tropo periods during the week. The rain events are unreliable with marked changes in outcome from run to run of the forecast models, but may provide occasional opportunities for rain scatter on the GHz bands.

The main Sporadic-E season has pretty much finished and, although occasional outliers can still provide activity into September, the events may be very brief. Of course, random meteor scatter and auroral propagation modes are always possible. For one reason or another, it is good to periodically check the VHF/UHF beacons; they are there for this very purpose. Perhaps now is a good time to update your VHF/UHF beacon list by looking at the real time, updated lists at to ensure you are there for the next chance opening!

Random meteor activity is still high and there is just one small meteor shower again this week. The September Epsilon-Perseids have a low Zenithal Hourly Rate of five. It is active from the 5th to the 21st of September, reaching a maximum on the 9th at 1100 UTC.

Moon declination goes negative again on Wednesday so we’ll have decreasing peak elevations shortening Moon visibility windows. It reaches perigee on Saturday so path losses will be getting lower all week. (

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