Propagation News – 3 December 2017

HF propagation for last week’s CQ Worldwide CW contest was fair to middling. There was a 10 metre opening on Saturday, but otherwise the money bands were 20 and 15 metres during the day, with 40 and 80 metres coming into their own after sunset. The predicted poorer geomagnetic conditions on Sunday didn’t really materialise, but it was interesting to see how quiet the bands were on Monday—after the contest had finished. It is amazing how contest activity can really show that the HF bands are actually open!

Otherwise, last week the solar flux index remained in the low 70s while geomagnetic conditions were mainly settled. Tuesday and Thursday saw the K-index climb to four and five respectively, the latter event probably caused by a glancing blow from a relatively weak coronal mass ejection (CME).

As we head into December you will find that 20 metres now opens later and closes earlier, often around or before sunset. But the lower bands really start to deliver, with 40m and 80m offering long periods of DX after dark. Top Band, as 160 metres is often known, can also offer DX for those equipped for 1.8MHz.

If you are using a VOACAP-based propagation prediction program, the predicted smoothed sunspot number for December is 13 using the McNish and Lincoln method. NOAA predicts the solar flux index will remain in the low 70s, but we may be set for poor geomagnetic conditions at times. The K-index is predicted to reach a peak of six some time from Monday to Thursday, due to a large coronal hole rotating into an Earth-facing position. Expect the possibility of pre-auroral enhancements, but ultimately depressed maximum usable frequencies and auroral conditions.

VHF and up

The weekend starts with a cold northerly pattern with wintry showers in eastern coastal regions giving some rain scatter. But this will soon fade as high pressure becomes more dominant by Sunday and through a large portion of next week. This is potentially good tropo news for the RSGB 144MHz AFS contest on Sunday the 3rd, especially for stations in the west and south. As the high develops, the subsidence inversion may provide some extended paths, especially midweek as the high starts to decline. The favoured areas will be over southern and south-western UK, but many places could do well for a time, especially if we have some overnight mist and fog, which in December can last well into the morning. Later in the week it will turn more unsettled again so it’s unlikely the tropo will last to the following weekend.

Now to meteor scatter. The Geminids have a broad peak, culminating on 13 and 14 December. This is usually one of the best showers of the year, with a maximum Zenithal Hourly Rate (ZHR) of 120. This week, in the run-up to the maximum, we can expect many useful reflections. Also remember that the minor shower, Puppid/Velids, with its low ZHR, will peak around Saturday the 9th. Early December has a number of other weak showers, so the meteor scatter enthusiasts should see some nice reflections throughout the week.

Sunday’s full moon is known as the Cold Moon and is also a supermoon. It is the only visible supermoon of 2017. The Moon will be closest to Earth so it will appear large in the sky. As it is at perigee path losses will be at their lowest, enabling smaller EME stations an ideal opportunity to work other small stations.

Category: GB2RS Propagation News