RSGB
GB2RS News Team | October 3, 2025
Last week was characterised by very unsettled geomagnetic conditions with a Kp index that reached 7.33 on 30 September and was often above 5.
This is not good for HF propagation!
But what caused this? A high-speed solar wind stream at around 750 kilometres per second, coupled with the Bz component of the Sun’s magnetic field pointing south, led to the disruption. But there didn’t seem to be any particular solar event that triggered the high-speed solar wind stream.
The Russell-McPherron effect is probably to blame. This is a phenomenon where the alignment of the Earth’s and the Sun’s magnetic fields, during the equinoxes around March and September, allows charged particles from the solar wind to more easily penetrate the Earth’s magnetosphere.
This enhanced connection leads to more intense geomagnetic storms and increased aurora activity as the Bz aligns favourably with the Earth’s magnetic field at these times. This may pass as we get further into October.
As a result of the geomagnetic storm, maximum usable frequencies, or MUFs, have often been lower than normal. A quick listen on 28MHz on Wednesday 1 October confirmed the poor conditions. It’s a shame as October is normally a fantastic month for HF DX.
The solar flux index peaked at 187 on 30 September, having been above
170 since 28 September.
Next week NOAA predicts that the solar flux index will remain above 150 to 160 all week. The good news is that geomagnetic conditions are forecast to improve, with a maximum Kp index of 3. If that comes to pass, we can expect HF to be better after a day or two, and we might be able to make the most of the autumnal conditions for DX.
VHF and up:
The current spell of unsettled weather, mainly over northern areas, is typical of the season, but it’s also common to find high pressure passing by in between the deeper lows. In the current pattern, the highs are mainly for the southern half of Britain. This will bring some good Tropo conditions at times for the VHF and UHF bands.
As we head into autumn, these lifts may linger through much of the morning on some days before the temperature rise breaks down any temperature inversion. A good clue is that it’s usually over when the overnight fog clears.
On the other hand, there will probably be some good rain scatter opportunities on the GHz bands as the active lows push fronts across the country, especially in the north. There are signs that we may return to high pressure over the country during the RSGB 2025 Convention weekend from the 10 to 12 October.
We have a meteor shower to play with during the coming week. The Draconids peak on Wednesday 8 October, but the shower stream is spread over the whole of the week.
Lastly, there have been some reasonable auroral events recently so, as usual, keep a watch on the Kp index going over 5 since, as we said earlier, these autumn months are very much favoured for auroral activity.
For EME operators, the Moon’s declination is increasing and goes positive tomorrow, the 6 October, so lengthening Moon windows and increasing peak elevation is the story for the coming week.
Path losses continue to fall as we approach perigee on 8 October. 144MHz sky noise will be low for much of the next seven days.
https://rsgb.org/main/blog/news/gb2rs/propagation-news/2025/10/03/propagation-news-5-october-2025/
(Mike Terry, UK/BDXC)
