Propagation News – 1 November 2020

RSGB
October 30, 2020

Last week saw more evidence that Solar Cycle 25 is definitely under way. Large sunspot group 2778 caused the solar flux index to rise to 82. And it then got even better when it was joined by active region 2779, which pushed the SFI up further to 88 on Thursday. This is the first time we’ve seen the SFI in the 80s for some time and a clear indication that things are changing for the better.

Both regions were responsible for B and C-class solar flares, but nothing that impacted the ionosphere too much. In addition to the sunspots we did have the lingering effects of a high-speed solar wind stream from a coronal hole, which saw the Kp index rise to four across the weekend.

This corresponded with the SSB leg of the CQWW contest and did have an adverse impact on propagation.

The elevated Kp index continued until late in the week and was still at three on Thursday, preventing the ionosphere from completely recovering. Nevertheless, propquest.co.uk shows that over a 3,000km path maximum usable frequencies often exceeded 24 and even 28MHz at times. Ten metre FT8 proved popular with the eastern states of the USA, Mexico, South America, Cuba, Malawi, Kenya, South Africa, as well as India, Malaysia and Papua New Guinea all being logged on Thursday.

As for next week, the STEREO ahead spacecraft shows a couple of sunspots returning to the Earth-facing solar disk. Regions 2775 and 2777 are coming back, but it is difficult to know how active they will be.

So as we enter November, NOAA predicts the SFI will be roughly 74-75 with quite calm geomagnetic conditions. The Kp index is predicted to be two by Monday, which bodes well for HF.

With the seasonal improvement in ionospheric conditions, a quiet geomagnetic field and possible sunspot activity, the next seven days could be quite good for HF propagation.
VHF and up:

We ended the previous week with very unsettled conditions bringing rain and strong winds at times. This pattern will continue into the first half of next week, so once again we expect GHz bands rain scatter to be on the propagation guest list.

There is a suggestion that a ridge of high pressure will move into Scotland midweek, gradually extending its influence southwards to make tropo a consideration. That said, the ridge may get overwhelmed by returning low pressure next weekend.

Recent unsettled weather, which is usually driven by strong jet streams, would be perfect for summer sporadic E, and it’s worth saying that even out of the traditional sporadic E season, FT8 may bring the occasional surprise. Definitely worth a periodic check on 10m and up.

The Moon’s declination is still rising, reaching maximum late on Thursday, so Moon visibility windows continue to be long. The Moon is just past apogee so path losses are still high. 144MHz sky noise peaks at 500K on Wednesday.

Continue to keep an eye out for low-VHF auroral propagation and remember, we are just over two weeks from the peak of the big Leonids meteor shower. (rsgb.org)