To state it simple, more or less we have understood that the propagation on amateur radio bands, especially those in the HF range, depends on the quantity of sun spots (Sn, Sunspots number): more the sunspots (higher Sn) means better propagation of electromagnetic waves and higher maximum usable frequency (MUF). The wise Old Men tell us that this sunspots number or, better, its daily and monthly mean, in the long term has a cyclic trend, that is it reaches a peak in a relatively short time, and then it has a long decay, which lasts several years, with a low sunspots number resulting in mediocre propagation. Such a trend, is recurring roughly every eleven years as we observe in the following chart showing the monthly mean susnspots number in the latest five cycles.
Poor us, we are now living the long low sunspots tail of the 24th solar cycle - few sunspots, low propagation… What we all wonder is: when the sunspots number is going to grow again? In other words: When is the new solar cycle going to begin? And, even more interesting: When is the propagation going to improve so that we could finally have DXing from our normal QTHs, with affordable power and antennas? To answer those questions, we get some help from the predictions published by prestigious research institutes.
Here following, I report two graphs, made available by the Royal Observatory of Belgium - Brussels - that show:
Above: predictions dated 2019 January 8; below predictions udatrd monthly. Credit: SILSO data/image, Royal Observatory of Belgium, Brussels.
- with a blue line, the monthly mean sunspots number (observed in the past); - with a black line, the trend of the monthly mean sunspots number (i.e., the same as the blue line but, somehow, smoothed); - with a red line the prediction, calculated through the standard method, of the monthly means sunspots number trend (therefore this is a forecast, what we are going to expect in the future); - with a green line, the prediction, computed through the combined method, of the monthly mean sunspots number trend (also this one is a forecast referred to the same interval of time as the red line, but it's based on a more complete mathematical model).
What is the difference between the two prediction methods? Which, out of the two methods is the correct one for the days we are living rigth now?
The standard method (SC = Standard Curves) consits in the interpolation of the Waldmeier standard curves; in short, this method is based on the series (which is the succession of numbers, put one after another, until now) of the amount of sun spots. The resulting curve (the red one) is a good prediction in those times when the trend is relatively smooth itself, when inversions of trend are not expected (that is, we are relatively far away from peak and from minimum, which are the two situations when we would expect a change of trend, in particular from decreasing to increasing in a period like now, between two solar cycles). In the end of the day, this method does not suit very well to the solr cycle phase that we are living right now.
The combined method (CM = Combined Method) combines a regression technique applied to the series of sunspots amount with the aa geomagnetic index, used as precursor for predicting the maximum value of the next cycle. This method, due to K. Denkmayr e P. Cugnon, provides a better prediction during the minimum phase between solar cycles, exactly what we need for these months (or years).
I suppose that the light red area in the left chart, and the light green area in the right chart, highlight the uncertainty bands, by which the actual trendline should stay within a certain (high) level of probability. The uncertainty band of the left chart is far larger than the one of the right chart because this uncertainty depends on the used method too. Let's say that, the prediction to be credible from our point of view, the two bands should be compatible, that is they should partially overlap or be contiguos along one border.
Finally, we can draw the conclusions we are interested: we relay on the charts dated January 8th, 2019, that are the one available in the moment I'm writing this article. Well, the standard method prediction is worrying us a little bit because it forecasts a flat 2019 an let us glimpse a possible recovery by the beginning of 2020, while the prediction with the combined methodlet us bode well in terms of increase of sunspots number and, thus, in terms of improving of electromagnetic waves propagation, beginning in 2019 spring!
Today I have added the two charts, similar to those, already commented, dated January 8. These new graphs are referred to the actual situation in the moment you are reading this article (they should update themselves at least monthly, at least until the link to SILSO will not get broken). I think that comparing the forecast shot in January 2019 with the actual one is very interesting, so that we can realize if the predictions work or they don't. For example, March 1st data show an absolute minimum (in the 24th cycle) of monthly sunspots number recorded in February; the standard method now confirms the prediction of a year 2019 flat on minimum and a recovery at beginning 2019.Instead, the combined method still forecasts a good recovery, starting in April 2019, and marking the 25th solar cycle begin. Let's see which method will reveal to be better than the other. Whatever is goin to happen, make sure to be prepared!
I'm adding another "live" chart that represents the daily sunspots number (Yellow line), monthly mean (blue), smoothed monthly mean (solid red), prediction with standard method (red dash and dot") and prediction based on combined method (dashed red).