Are we approaching the 'solar minimum'?

Maybe!

There are increasing comments on many active ham radio and space-weather websites that suggest that the solar minimum (of the current cycle) is approaching. Spaceweather.com has a chart (derived from a NOAA chart) which illustrates the current situation (on the right).

This prevailing view amongst spaceweather professionals and specialists is that the current trend indicates a 2019 may see the turning point after which conditions may improve.

The real problem with this is that trend analysis also suggests that recovery from the minimum may be slow and weak. In the last few years the sun has been much more unsettled as the solar minimum approaches and therefore less predictable with any certainty - but that is always an issue even in the middle of a cycle (see 2013 on the NOAA chart).

Below is a compilation of daily Critical Frequency (foF2) charts for Chilton UK covering 15 August to 15 November in 2016 & 2017.
A few trends can be seen, not least that the incidence of distrubances from Coronal Hole (CH) activity may be ameliorating slightly. However, although there has been a decrease in the size of Coronal Holes (January - February 2018) and they have been at the poles rather than the equator (typical of the onset of the solar minimum), here has been an increase in the number of small holes giving short duration discharges. In effect, which conditions have generally been poor, the hourly differences have been quite variable leading to (at times) a wildly unstable ionosphere.

This chart, compiled by PARC from UKSSDC data shows the daily variation in Critical Frequency in January & February 2018):


In the charts below, September to October 2017 was more settled than in 2016, but started with the maximum daily foF2 being a little weaker. There are some indications that CH activity has is decreased a little in both frequency and amplitude. There are greater differences in the October-November periods for each year. 2016 showed at least 5 major CH events which resulted in wide variability in the foF2, with clear evidence of enhanced foF2 a day or so before the CH disturbances started.

In contrast, October to November 2017 has been much more stable overall, compared with 2016 - and with maximum foF2 well over 7Mhz for many consecutive days . . at least up to 6 November when a cluster of CHs pushed the foF2 well below 6MHz. A steady rise in max. foF2 since 15 November could again be badly affected by CH activity in December 2017, but there are indications that CH events have become less frequent and of lower amplitude since September. Together with winter conditions this has given somewhat better HF propagation in November 2017 compared with 2016.

While it isn't possible to predict solar conditions ahead into the mid-winter and early Springtme, the current trend seems to offer some hope that CH's are generally becoming a little less severe and less frequent. However, the possibility of further amelioration - if not improvement - in solar conditions into Springtime simply cannot be predicted.

So, the answer to the question: Are we approaching the 'solar minimum'? is that the scientific consensus is that the minimum is quite likely to be more than a year away, and even then the next cycle could be both short and just as weak as the last one.
What looks like a respite at present may just be very temporary.


Click for full size image. Data from
  UK Solar System Data Centre