Propagation News – 6 January 2019
A new sunspot appeared this week, although it belongs to outgoing cycle 24 and is therefore not a sign that the new cycle 25 is under way just yet. We may still have to wait until at least the autumn before that happens. Despite pushing the solar flux index up to 75 on Thursday we are still very much in the mid-winter doldrums, with bands opening late and closing early. Having said that, there have been reports of some early afternoon 17m transatlantic CW openings to the USA. 20m and 40m have often closed early, but it is worth checking both bands after dark—there has been some activity spotted on 40m around 11pm so it is worth looking.
A large solar coronal hole became Earth-facing on Thursday, which may cause some disruption to the bands at the weekend, potentially pushing the K-index to four with depressed maximum useful frequencies. Once its effects have passed we should see more settled bands, with a maximum K-index of two next week and a solar flux index of around 71.
Daytime critical frequencies are currently reaching a maximum of about 4.9MHz, meaning 80m remains the best band for daytime NVIS or close-in signals. Sixty metres or 5MHz may also be fine for inter-G signals, although you may struggle on 60 metres at times with stations closer than about 100km.
Over longer distances, 20 metres remains favourite, with possible occasional openings on 17m. Winter sporadic E may throw up some surprising openings on 12 and 10 metres, but these may be fleeting and hard to predict.
VHF and up
There is still a large area of high pressure on the charts, and as is typical of such features they can be very persistent. This one is going for the long game with another one to two weeks of high pressure weather to come. This means that tropo will be the mode of choice, with variations mostly down to how moist the air near the surface is compared with the very dry air just above the temperature inversion. A big contrast in moisture means better ducting on VHF and UHF and the best sign of this is when you find mist and fog forming—bad for travelling but better for tropo.
The position of the high is crucial and when we find a cold northerly flow pattern with the high just to the west, this tends to reduce the prospects for good tropo, despite the pressure being fairly high; so expect variations in the scope and intensity of the openings as the high centre drifts around the UK.
Out of season sporadic E is always worth checking for during the depths of winter, especially with the big changes in the wind regime in the stratosphere at the moment.
The short and intense Quadrantids meteor shower last week usually ushers in a quiet period of meteor activity until early April so keep looking for the usual dawn enhancement of random meteors.
The Moon reached its lowest declination yesterday and apogee on Wednesday, so there are short moon windows with low elevations and high losses this week.
Category: GB2RS Propagation News
