Propagation News – 19 August 2018
Matter from a solar coronal hole sent the K-index to four on two occasions last week. This adversely affected the ionosphere and on Thursday morning the maximum usable frequency over 3,000 kilometres was struggling to get much above 10MHz. Earlier in the week conditions had been much better. In fact, there were signs we are now moving towards more equinox-like HF conditions and away from the summer doldrums. Chris, G0DWV reports working a number of Japanese stations on 17 metres last week, while Andy, M0NKR worked as far west as Montana in the USA. Checking the bands before retiring on Wednesday evening, Steve, G0KYA was surprised to hear a loud XQ3SK in Chile at the bottom end of 20 metres at 2230UTC. This does bode well for HF over the coming weeks, as long as geomagnetic conditions can remain quiet.
There was one tiny visible sunspot group last week, which pushed the sunspot number to 12, but there are no signs of any others coming around the sun’s limb. Consequently, next week NOAA predicts the solar flux index will be around 68-70 again, with minimal or zero sunspots. It also predicts unsettled geomagnetic conditions on the 20th and 21st due to a high-speed solar wind stream from a coronal hole. Conditions should be more settled after that, so we may expect better HF conditions from Thursday onwards.
VHF and up
This weekend a weak low over the country may lead to some short sharp scattered showers, setting up conditions for rain scatter on the microwave bands. The many weather radars available online will allow you to follow these large highly-reflective cumulonimbus clouds to set up those longer-range microwave paths.
Subsequently, southern Britain will have a ridge of high pressure pushing in from the Azores high and this will re-introduce the prospects of some tropo, especially to the south into the continent and across Biscay to Spain or even beyond, as we’ve seen this last week. There will, however, be a tendency for lower pressure to the north of Scotland, keeping winds stronger and curtailing the chance of tropo.
Lastly, sporadic E has been looking a bit thin recently, although a few openings were seen at the end of last week. Unfortunately, any favourable placements of jet streams this weekend will soon be displaced and the next week is showing only limited potential with a very weak upper air flow over Europe for much of this week.
The Moon is at minimum declination on Wednesday and is at its apogee of 405,700km on Thursday. This means the worst EME conditions of the lunar month this week, with highest path losses and very short, low-elevation moon visibility windows.
Category: GB2RS Propagation News
