domenica 2 aprile 2017

Propagation News – 2 April 2017

Last week was a mixed bag. As predicted we had geomagnetic storming, thanks to the effects of a large coronal hole and its associated high speed solar wind stream, but we also had some good HF conditions at times. With the solar flux in the low 80s, propagation was dominated by the impact of solar material on Tuesday, with the subsequent rise in the K index to five and even six. The initial onset brought a pre-auroral enhancement, with many stations reporting good HF conditions. But this was soon tempered by poorer conditions later in the week.

Visible auroras were reported at higher latitudes and a UK-wide red aurora alert was issued by Lancaster University on the 27th. Next week, NOAA predicts that the solar flux index will decline into the mid 70s.

Geomagnetic conditions will remain unsettled until later in the week, with the K index likely to hit four at times. We may then get a bit of a respite, with more settled conditions on Friday and across the weekend of the 8th and 9th. You can then expect maximum useable frequencies over a 3,000km path to hit 18 or perhaps even 21MHz at times. We won’t see any significant activity on 10 metres until the Sporadic-E short-skip season starts in a few weeks.

VHF and up:

Two widely-used weather models are predicting a developing high just after the weekend. One has it starting today. For the VHF, UHF and SHF bands, this means a good week with the prospect of some useful Tropo once the unsettled weather at the start of this weekend has moved away. Most areas are likely to benefit from Tropo paths within the UK, across the North Sea and down to the south across Biscay.

There are often two temperature inversions in this type of pattern, one due to the high itself, producing an elevated duct somewhere between 1km and 2km in height. The second type is often found near the surface at the end of a night time of cooling. This one is less reliable, since it will often disperse after the sun begins to lift the daytime temperature. This tropo should make the 144MHz UKAC and FMAC contests very interesting on Tuesday evening.

Isolated heavy showers this weekend might have brought rain scatter, but they’ll be gone by the start of next week.

The Sporadic-E season has not quite started yet, but it can’t be far away.

The Moon is at high declination early this week, so long windows of moon visibility. We are past perigee, so losses will increase as the week progresses.