Propagation News – 2 September 2018

Just after we filed the propagation report last Friday we heard that a new large sunspot had just appeared. This pushed the solar flux index to 72, but more interesting was the fact that it appeared to have a reverse magnetic polarity to the rest of the spots in solar cycle 24. This means it may be the second spot seen of the new solar cycle 25. Time will tell, although this doesn’t necessarily mean that the new cycle is about to burst into life. We may still be at sunspot minimum for another 12 months or so.

Also last Sunday saw the Kp index rocket to seven due to the effects of an incoming high-speed solar wind stream. This was unexpected and caught space weather watchers unawares. It has now been linked to a coronal mass ejection that occurred earlier in the week that scientists didn’t think would impact the Earth. This just goes to show how hard it is to predict what the Sun is going to do one week in advance! The CME knocked the bands for six last weekend with a virtual total lack of signals across HF most of Sunday. With this information we are cautious about predicting what will happen over the next seven days!

What we can say is that the Sun is likely to remain fairly spotless, so the risk of solar flares is minimal. Sunspot number 2720, which did spark a number of flares on Friday, the 24th, has now rotated out of view, leaving a fairly blank canvas. Maximum usable frequencies are therefore due to return to seasonal averages, with 20 and perhaps occasionally 17 metres providing the most HF DX.

We are now moving towards the autumnal equinox so north-south paths may also start to improve, but we may have to wait another month or so for an improvement in east-west paths, such as UK to North America.

VHF propagation news

Last Sunday’s 10GHz contest saw some excellent rain scatter propagation over the UK, with QSOs well up to the 400km mark. But the next spell of weather is looking much more settled with high pressure on the charts for much of next week. This could bring tropo back on the agenda for most areas of the country at times. That makes it a good week to get down to the multimode ends of the bands on VHF and UHF. Remember, tropo is a relatively long-lasting mode, so there is plenty of time to make the QSOs, unlike sporadic E, which can be very transient indeed. Also unlike sporadic E, tropo tends to get better on higher frequency bands, so 23cm is better than 70cm, which is better than 2m. The sporadic E season is just about over for this year and, although there can be openings into early September, they are hard to find and usually short-lasting.

Our most predictable propagation source, the Moon, is at positive declination all week and reaches perigee early on Saturday morning so it’s a good week for EME tests, with long availability and low losses. The Moon follows a 28-day cycle, where the plane of its orbit moves from south of the equator or negative declination, to north and back. Its distance from the Earth changes from closest or perigee to furthest, apogee.

Currently maximum declination and perigee almost coincide, favouring stations in the northern hemisphere, but this difference drifts slowly. By 2022 this situation will have reversed and southern hemisphere stations will get this coincidence.

Category: GB2RS Propagation News