Propagation News – 12 April 2020

| April 9, 2020

Sunspot group 2759, as reported last week, never really amounted to much and vanished before it got to the solar disk’s edge. The matter from a solar coronal hole did hit the Earth last weekend as we predicted, sending the Kp index to four in the early hours of Saturday morning. Even though we don’t have any sunspots, we are now benefiting from seasonal changes in the ionosphere and longer days.

Monday’s 80m CW Club Championship contest saw the critical frequency stay comfortably above 4MHz, which guaranteed a lively event with high scores all round. Stations in the Netherlands, Czech Republic, Sweden and France joined in, which made for some head-scratching for amateurs expecting to hear mostly UK-based call signs.

But daytime on HF is still a little lacklustre as we continue towards sunspot minimum. Next week, NOAA predicts more of the same with the solar flux index pegged at 68 and zero sunspots. The Solar Dynamics Observatory spacecraft showed a large coronal hole was Earth facing on Thursday, which suggests we might get disrupted conditions over the weekend.

Although we don’t know the solar matter’s expected Bz signature, if its locked-in magnetic field shows a strong south-facing Bz component we can expect it to couple strongly to the Earth’s magnetic field, resulting in a raised Kp index. So look out for the possibility of a pre-auroral enhancement at first and then auroral conditions on 10m as it progresses.

Meanwhile, there are signs that this year’s sporadic E season could soon warm up. Some Spanish low-power beacons have been spotted on 10 metres, but they are currently quite weak. We expect Es conditions to improve towards the end of April or early May with daily short-skip openings out to around 1,500 miles. So it is a good time to make sure your 10m antennas are working properly before the Es season starts.

VHF and up

In a general sense, this period of weather is essentially high pressure-driven except for a couple of brief incursions from low-pressure systems. Easter weekend sees the first visit by a low drifting from the north with April showers and some rain scatter potential. This is followed by a high moving from north-west Scotland south-east into Germany and again producing some good tropo potential, which may well coincide with the 70cm UKAC on Tuesday evening, so a good result.

The second half of the week models show a low moving from the south and affecting the southern half of the UK bringing some showery rain, perhaps thundery, so again some more rain scatter on the microwave frequencies.

Lastly, the following weekend sees high pressure returning to Scotland and later the North Sea with further tropo options.

As we are pushing well into April we can expect to see the new sporadic E season developing in the next couple of weeks and the Easter Sunday 50MHz contest could well flush out any early stirrings!

While we are still close to Lunar perigee, losses are low, but Moon declination is minimum on Tuesday. Moon visibility windows are just a few hours at low elevation, making EME difficult due to ground noise. Added to this is high 144MHz sky noise in the first part of the week, making it a poor week for EME.

This Thursday sees the start of the Lyrids meteor shower, so we are coming out of the period of low meteor activity. Keep checking around dawn for the best random meteor contacts.

Overall it’s a good week for activity on the VHF/UHF bands.

Category: GB2RS Propagation News