RSGB
GB2RS News Team | September 12, 2025
As of Thursday 11 September, it looked like someone had thrown a switch on the Sun to turn off all new sunspots! Unless there is a big change, there will be no sunspots visible on the Sun’s surface today, the 14 September.
It is clear that we are no longer at solar maximum.
A bigger problem is a large coronal hole on the Sun’s surface, which is rotating to be Earth-facing. It is on the Sun’s equator so is ideally placed for maximum disruption to the Earth. A high-speed solar wind stream should reach Earth by the 14 September, and geomagnetic storming may be possible at higher latitudes. Expect maximum usable frequencies, or MUFs, to drop and trans-polar paths to be affected once the Kp index rises.
HF is now starting to improve as we head towards mid-September. By 1000UTC Propquest shows that the MUF over a 3,000km path can be as high as 31MHz, as long as the Kp index stays low. This should continue to improve as we head into October.
The best DX last week continued to be T30TTT in Western Kiribati, this time on the 40 and 17m bands using FT8. 9J2FI in Zambia also put in an appearance on the 17m band using FT8. TZ4AM in Mali was spotted on the 15m band using SSB. For Morse enthusiasts, HC5AI in Ecuador was working on the 15m band using CW, according to the CDXC Slack chat group.
NOAA predicts that the solar flux index will start the coming week at 125 but then gradually improve to reach 145 by the end of the week. As mentioned earlier, the Kp index is set to reach 4 or 5 between the 14 and 16 September due to the coronal hole.
VHF and up :
The present spell of unsettled weather is likely to remain the main driver of weather-related propagation modes for the next week. Low-pressure systems are following the jet stream across the Atlantic and over the UK, which is a typical track for this time of the year. This means that we should expect to experience the odd example of rain scatter for the GHz operators, and occasional strong winds will start to test that we have our antennas in good order after the quieter weather during the summer.
This is not to say that there won’t be any Tropo but we will have to look for it carefully. In a mobile weather pattern such as this, the periods of high pressure tend to act as separators between the lows and, as a result, they usually move with similar speed. This makes them short-lived and thus not particularly good at establishing strong inversions for Tropo. There are two low-grade possibilities. One is around Tuesday 16 September as a weak transient ridge moves across the country. The second will be as another weak ridge moves across on Friday 19 September.
The meteor scatter situation is still pretty much in a random activity state, although there was a minor shower of the Epsilon Perseids, which peaked on the 9 September and may have a few left in the tail-off. However, in general, it’s more realistic to assume we’re dealing with random activity. Aurora, on the other hand, has been putting in an appearance lately, so keep watching the Kp index for values climbing above 5.
Now for an update on EME. Today, the 14 September, marks the Moon’s maximum declination – its highest point in the sky. Perigee, when the Moon is at its closest point to Earth, was passed on 9 September, so path losses are increasing. Sky noise is low and will remain so until the 20 to 22September when the new Moon is very close to the Sun.
https://rsgb.org/main/blog/news/gb2rs/propagation-news/2025/09/12/propagation-news-14-september-2025/
(Mike Terry/BDXC)
