Propagation News – 29 November 2020

Last week represented a good example of how solar cycle 25 is progressing. We started the week on the 22nd with a solar flux index, SFI, of 88 and a sunspot number of 35. Just to recap, that doesn’t mean there were 35 sunspots, as we count each sunspot group as 10 and each spot as one. But, by Thursday, the SFI was up to 104 with a sunspot number of 40, and there were three large groups visible on the Sun. As well as pushing up the SFI, the spots have been very active on the solar flare front, with daily B- and C-class flares being emitted, although their effects on the ionosphere have been minimal luckily.

With the CW Worldwide CW contest occurring this weekend, this SFI does bode well for HF propagation. With zero coronal holes appearing, at least on Thursday, and the possibility that the SFI could rise even further in the coming days, this looks like a good combination for one of the best CQWWs we’ve seen for a few years. An SFI of more than 100 virtually guarantees some F2-layer propagation on 10 metres. These openings may be short-lived as the MUF drops a little, but it is definitely worth keeping an eye on 28MHz at times, especially near noon on North-South paths.

If you are planning to take part, it is a good idea to plan your activities using a tool like predtest.uk. Typically, on the higher bands, such as 20, 15 and perhaps 10 metres, you will work stations to the east of the UK in the morning. As noon approaches, propagation will swing south. And the afternoon will be optimum for contacts with the USA. For 40 and 80 metres the opposite is generally true, where you should be looking for a night-time path between you and the station you wish to work.

Even if you hear this broadcast on Sunday it isn’t too late to take part, as the contest runs until midnight. Do get on as there is usually a lot of activity and it is a great opportunity to increase your country score.

VHF and up:

The background weather pattern is again looking like high pressure will predominate, with a good prospect for Tropo. It will be a typical spell of November quiet weather with frost and fog overnight, perhaps lasting through the day in a few places.

This prevalence for cool moist air near the surface makes for good Tropo, since you will often find the high pressure has produced a layer of warmer and drier air above the inversion. It’s the contrast that changes the refractive index of the air and can create ducts for VHF/UHF DX propagation. We should point out that some models allow the high to collapse in the second half of next week, so it’s worth following the daily forecasts as we go through the week.

Just one minor meteor shower this week. The Phoenicids peaks on the 2nd with a variable zenith hourly rate, but its radiant is not visible from the UK.

The Moon reaches maximum declination on Wednesday, so we have long visibility windows all week with falling path losses. 144MHz sky noise is moderate to low all week, but rising up to 500 kelvin on Tuesday.

And that’s all from the propagation team this week. (rsgb.org)