Propagation News – 5 April 2020

| April 3, 2020

The high speed stream of solar particles from a coronal hole on the Sun last week wasn’t moving as fast as we initially thought. As a result, its impact on Earth, and the subsequent rise in the Kp index to four, happened in the early hours of Tuesday morning and not the weekend as we predicted. The impact though was relatively short-lived and by late Tuesday the Kp index was back down to two.

The bands were affected though, with the critical frequency as measured at Chilton struggling to reach 5MHz until midday Tuesday. The predicted MUF over a 3,000km path, according to, looked like a roller coaster ride, often exceeding 18MHz, but then crashing down to below 14MHz. A smaller coronal hole is now facing Earth, which could mean a higher Kp index over the weekend, although NOAA isn’t indicating this.

There is some good news though. A small sunspot group, numbered 2759, appeared on the Sun’s surface, pushing the sunspot number to 12. This represents two sunspots, which accounts for the two, in one group, which accounts for the 10. The spot’s high latitude suggests it is from the upcoming Solar Cycle 25. But on Thursday the SFI was still at a modest 69.

NOAA predicts that next week the solar flux index will remain at about 68-70 and geomagnetically the Kp index will remain at about two. The good news is there are signs that the higher HF bands are remaining open longer. As the season progresses this should improve, with 30m and even 20m eventually remaining open until very late. We are also heading towards the 2020 sporadic E season, which should bring strong short-skip signals on 10m, but more of that in the VHF section.

VHF propagation news

The weather produced some half-hearted attempts at tropo in the past week and even some weak sporadic E opportunities appeared on 10m and 6m.

This week looks to be rather mixed in a weather sense. The high will weaken and drift east allowing low pressure to move towards north-west Britain from the Atlantic with a series of fronts crossing the country next week. This will offer the chance of April shower rain scatter at times and then, by next weekend, there may be a rebuilding of high pressure to the east with a hint of tropo and warmth to end the week.

The month of April is traditionally the start of early sporadic E on 10m and 6m via traditional modes like CW and SSB. For example, a weak jet stream over the Pyrenees mid-week could favour paths to IS0, EA6, EA5, etc. Remember that springtime is also a good chance to get some auroral activity, so check those Kp values: anything above four or five is interesting.

Moon declination is positive until Tuesday, as is perigee, so losses will be at their lowest. Moon windows will shorten as the week goes on. 144MHz sky noise is low, so in all it’s a good week for EME. We are still in the annual low activity period for shower meteors until the Lyrids, which should start on the 16th of this month. Keep checking around dawn for the best random meteor contacts.

Category: GB2RS Propagation News