Propagation News – 27 August 2017

Last week saw the solar flux index touch 90 as large sunspot group 2671 rotated into the centre of the solar surface. But, unfortunately, the predicted unsettled geomagnetic conditions, caused by a high-speed coronal hole solar wind stream, pushed the K index up to six early in the week. This hampered DX by pushing maximum useable frequencies downward. The unsettled conditions continued until at least Wednesday the 23rd.

Sporadic-E did put in an appearance for last weekend’s International Lighthouse and Lightship Weekend, bringing short skip to the 40m band. This meant that many UK amateurs were able to contact special event stations on 7MHz that would have otherwise been unworkable, other than by ground wave. This was a good example of how Sporadic-E clouds over the UK can often bring advantages on the lower HF bands, such as 40, 30 and 20MHz, while we normally associate Sporadic-E with 28MHz and above.

This weekend there is a chance that a small coronal hole may threaten us with more unsettled geomagnetic conditions. Conditions may also be unsettled mid week due to the effects of another coronal hole, but could improve for next weekend’s HF SSB Field Day.

Next week sunspot 2672 will be fully facing Earth. This has already produced an M-class solar flare and a number of lesser C-class flares, so we may be in for a bumpy ride. However, NOAA predicts the Solar Flux Index will decline to the high 70s.

Maximum useable frequencies over a 3,000km path are still peaking around 17MHz during the day, with occasional DX openings on the 17m band.

For this week there is still a chance of limited Tropo options as a ridge of high pressure develops over southern Britain. As usual for Tropo conditions it is the higher VHF, UHF and GHz bands that fare best and, unlike with Sporadic-E, the openings can be long lasting, especially over sea paths. Night-time is often best over the land, since there will sometimes be a shallow surface temperature inversion to add to the one brought by the high pressure, giving longer paths.

The second half of the week may see the return of low pressure in the north particularly, but it will increase the chances of some rain scatter on the GHz bands.

Sporadic-E is now nearing the end of its main season and at the moment the jet streams look to be fairly weak, meaning Sporadic-E will struggle to make many appearances.

As we head into the week, a new Atlantic jet stream will appear over Scotland and Scandinavia, giving a chance of northern Sporadic-E paths into Scandinavia and across to the States. About this time there will also be a broad upper ridge over France and Germany, which may also help with Sporadic-E.

There are only minor meteor showers this week, so continue to look around dawn for the best random meteor scatter contacts. We have negative Moon declination this week and apogee on Wednesday. The moon doesn’t get above 20 degrees elevation after Monday and path losses will be high. For VHF operation, the low moon elevation means high ground noise in the beam of the antenna.

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

Category: GB2RS Propagation News