Solar cycle 24 minimum approaching fast - but there's hope on the horizon

13/04/201805/06/2022 g7lfcPosted in Latest, PropagationTagged 24, 25, hf propagation, solar cycle

There has been a noticeable downturn in HF propagation over the last few weeks, so much so that that even the number of FT8 stations available to work seems to have diminished since Christmas. According to a top contester, Frank Donovovan (W3LPL) (as reported in the 12th April edition of the ARRL’s weekly newsletter), more spotless days on the sun signals the start of a lengthy and deep solar minimum phase.

Apparently, recent sunspot numbers have been very low and there doesn’t appear to be any prospect of them getting much better in the near future. No sunspots were recorded at all over the week of the 5th to 11th April and low solar flux levels don’t show any sign of increasing over the next month, or so, either. However, we’re not at solar solar minimum yet so we can only imagine that things have yet to get worse before they start improving.

Solar Cycle 24’s minimum period started during the June of 2016 when 8 consecutive spotless days where recorded. However, there were only a total of 32 spotless days in the whole of 2016, so when March 2017 saw 15 consecutive spotless days recorded, followed by relatively infrequent spotless days for the next 7 months, we knew we were well on the way to this current solar cycle’s minimum phase. A further extended period of 13 consecutive spotless days occurred last November and this has been followed more recently by many more spotless days. 2017 saw a huge increase over the previous year with 104 spotless days.

When I started operating using the FT8 mode at Christmas, I was impressed with the contacts being made, despite the poor solar conditions and my modest set-up, and that impression was carried on throughout January and February. Contacts using other modes were much rarer so I was glad that I had discovered this new ‘magic’ mode to keep me going for the next few years on the HF bands. However, even I noticed a good drop in HF propagation levels during March and this is confirmed by Donovan’s observations. He noted that there was a significant increase in the number of spotless days when the total for the month reached 25; that’s just under half of the total number of spotless days for the first quarter of the year. Comparing this data to that from the period of September 2007 through to January 2009, at the end of the last solar cycle, Donovan predicts that we have probably just begun a period of about two years that will see many more frequent spotless days, and this will include many more extended periods of consecutive spotless days.

Donovan reckons that, maybe, by the end of next year we will start to see the emergence of opposite polarity sun spots at high latitudes on the sun. Once these are observed they will signal that we are nearing the end of the current solar cycle and the end of the current period of solar minimum conditions some time afterwards.

It is Donovan’s belief that the number of spotless days during solar minimum, together with other factors, can be used to predict the likely strength of the next solar cycle. He reports that the current intensity of the sun’s magnetic field is stronger than it was at the same point in the previous solar cycle and predicts that, if the extended periods of consecutive spotless days end in about a year’s time, the next solar cycle will be stronger than the current one. However, if they take more than two years to end he believes that solar cycle 25 will be weaker than the current one; that would be a disaster for HF operators who have already suffered a number of years of poorer propagation than we have come to expect.

At the end of the day, it’s all speculation at the moment and nobody can really predict what’s going to happen with any certainty at this point, but there does appear to be a glimmer of hope that solar cycle 24 levels of HF propagation won’t be repeated again within the next cycle. I guess we’ll have to wait for another year, or so, until we can start to make more accurate predictions.