Solar Cycle 24 continues on its way to a Sunspot minimum. The thirty day average Sunspot number for September (Ri) was 44.7, a little less than the August number of 50. The black line of the chart Ri is the sum of the north and south solar magnetic fields. While a year or so ago, the southern magnetic field (Rsouth) was creating the majority of the Sunspots, the north magnetic field (Rnorth) is dominate now. In April the Sun had a period of low activity with a thirty day average of 20.9.
Looking at a comparison of Solar Cycles 23 and 24 shows that the Cycle 24 has been much less active than 23. This, of course, has prompted many to declare we are on our way to another minimum with corresponding cooling of global temperatures. But first a few comments on the difference one of the ways that Sunspots numbers are reported.
Looking at the far right of the chart, the black line is the monthly average Sunspot number and it is 44.7 as noted above. The red line is the official Sunspot number. It is a thirteen month lagging calculation. It is always 6 months behind the current date. It is the means by which the number is smoothed. The green line is a forecast of what it will probably be when the official smoothed number arrives at September 2016 . The green lines forecasts the September Sunspot number at 34.5. It will probably not be exactly 34.5 at that time but the difference will likely be small..
A comment on my blog by firstname.lastname@example.org provided a concise summary of the official number calculation methodology. It can be seen at the at the end of this blog.
Lastly as a reminder of how Cycle 24 looks in comparison to the preceding Cycles, the chart below gives the needed perspective:
This chart illustrates how much more active recent Solar Cycles have been in comparison to Cycle 24. Cycle 21 began in March of 1976. The peak International Smoothed Sunspot number for Cycle 21 was 232, Cycle 22 was211,Cycle 23 was 180 and Cycle 24 was 117.
A look at a Solar Cycle 25 projection is on my list of topics to post—hopefully soon.
All Charts a courtesy of Soleninfo/solar
International Smoothed Sunspot Number calculation.
The smoothed count is a 13-month averaged sunspot count using this Belgium’s formula:
Rs= (0.5 Rm-6 + Rm-5 + Rm-4 + Rm-3 + Rm-2 + Rm-1 + Rm + Rm+1 + Rm+2 + Rm+3 + Rm+4 + Rm+5 + 0.5 Rm+6 ) / 12
Rs = smoothed monthly sunspot count
Rm = One month’s actual sunspot count
The “-6” through “+6” appended to each Rm is the number of months before or after the month whose smoothed count is being calculated. The beginning and ending months in the formula are only given half the value of the others.