Propagation News – 27 December 2020

HF conditions were not terribly good over the last week with maximum usable frequencies down in general. The best DX has been on 40m, especially around greyline times, although there has been a little winter Sporadic-E activity on 10 metres as well that has seen Italy and Spain appearing on FT8, as well as Brazil on 10m via the F2 layer. The lack of sunspots has seen the solar flux index move back down to the low 80s again.

Solar matter from a coronal hole pushed the Kp index up to four late on Monday evening as predicted and on Tuesday the Kp index was still pegged at three for most of the morning. NOAA predicts that the solar flux index will remain in the 80s for the Christmas period, with active region 2794 helping to push it towards 86 over Christmas Day and Boxing Day.

Unfortunately, NOAA also predicts that a high-speed solar wind stream from a coronal hole may impact Earth over the Christmas period, so we may expect the Kp index to rise again to four or even five just before Christmas with detrimental effects on maximum usable frequencies. Look out for possible pre-auroral enhancements, although these are hard to predict.

This should start to settle by the 27th, with the Kp index predicted to go back down to two. So DX conditions may improve after that time.

There is little other festive cheer, with the SFI remaining in the low 80s for the rest of the month and into the New Year. Let’s hope 2021 sees the return of the upward trend of Solar Cycle 25 with an increase in sunspots and HF DX.

VHF and up

It’s looking like a predominantly unsettled period of weather over the Christmas holidays, with a ridge of high pressure to the west of Britain soon declining to allow low pressure to move in and reside over the UK for the bulk of next week. This has a chance of providing some good rain scatter conditions on the GHz bands.

Sporadic-E has a habit of appearing at this time of year. There is some work that relates the chances of Sporadic-E to disturbances in the stratosphere when the winter polar vortex breaks down in a feature called a sudden stratospheric warming, where temperatures can increase by tens of degrees Celsius over 24 hours.

This disturbance in the stratosphere can produce conditions where Sporadic-E is more likely because of the changed flow pattern. Check the usual Sporadic-E bands like 10m and 6m for signs of activity, especially during the first two weeks of January, but it is probably better to focus on the period 9am to 3pm rather than the summer pattern of mid-morning and late afternoon.

The Quadrantids meteor shower peaks between late-night on the 2nd of January until dawn on the 3rd with, a huge ZHR of 110. It is known for bright fireball meteors causing big over-dense radio meteor bursts. You have to be ready at the right time though, as the peak is very short, lasting just a few hours. This is because the shower is a thin stream of particles and the Earth crosses the stream at a perpendicular angle.

The Moon reaches maximum declination this Tuesday so visibility windows are long. Today we are at apogee so losses are high but 144MHz sky noise is low, not reaching 500 kelvin until Tuesday.

And that’s all from the propagation team this week.

Category: GB2RS Propagation News