Propagation News – 5 February 2023

Well, what a difference a few weeks make. On the 15 January, the solar flux index was at 234 and the Sun was peppered with spots. This week, on Thursday, the SFI was at 134 and the solar surface looked like it was at sunspot minimum again.

The Sun has also been mainly geomagnetically quiet, with a maximum Kp index of 3.67 on Thursday, due to an elevated solar wind speed with a southward pointing Bz. We have only had relatively minor C-class solar flares to contend with.

Meanwhile, there is DX to be worked, especially on 10m which continues to shine.

The good news is that this lull in solar activity should come to an end, although the Space Weather Prediction Centre predicts that the SFI may only go up to 155 next week. Unfortunately, it also predicts disturbed geomagnetic conditions, especially from the 7 to 10 February.

With the daytime critical frequency, as measured at Chilton, reaching almost 9.7MHz at times, we are virtually guaranteed good conditions on all of the upper HF bands with 10m predicted to be open for contacts over 3,000km for most of the day. Night-time highs are set to reach 9 to 9.5MHz over 3,000km. So, all frequencies, except 7MHz and below, are likely to be closed to DX.

80m may also close to short-range or near vertical incidence skywave skip at night, leaving only continental and longer paths, such as southern England to Scotland, open. This should improve as we head into Spring.

VHF and up

There is a continuing tendency for high pressure to dominate the weather charts and keep tropo on the agenda for much of the coming week, but with some caveats.

The position of the high is such that, as we end the current week, it’s over France and this puts us in a mild westerly flow with reasonable tropo propagation.

After this weekend, some weather models suggest a modest cold-air Atlantic high will arrive and will probably link with an intense high of more than 1050 millibars over western Russia. This may lead to a very cold easterly weather pattern over southern Britain by midweek with a chance of wintry weather and snow showers over eastern areas coming in from the North Sea.

This could be a good time to experiment with scatter propagation on the GHz bands. Note that winter showers generated over the sea are often twenty-four-seven phenomena rather than the traditional daytime showers used for rain scatter in the summer.

Keep trying other modes like meteor scatter around dawn and aurora when the Kp index is high, but the high-pressure-driven modes will be the primary focus.

For EME operators, Moon declination is still high, not going negative again until Thursday. So, EME Moon availability windows will shorten and path losses will decrease as the week progresses. 144MHz sky noise is low all week, only reaching 350 Kelvin next Sunday.

Category: GB2RS Propagation News