Solar Cycle 24 activity has peaked and it is on its way to a minimum. Of course the exact date of the minimum and the start of Solar Cycle 25 is not known. Because normal Cycle life is nominally 11 years, start of Cycle 25 should be in 2019, The Sunspot number (Wolf number 30 day average) for April was 38!! The chart below shows the rather sharp drop from March’s 54.9.
The black line (Ri) is the 30 day average—if you look carefully you will see it is the sum of the green line (Rsouth) and the red line (Rnorth). The dashed blue line is the “official Sun Spot number. It is the smoothed count of a 13 month average monthly Sunspot count divided by 12. The oldest and newest monthly count are reduced to half and the other numbers are given their full count. And is always 6 months behind the most recent month. This is the way it has been done for many years; hence it has a history record to use for comparing Solar Cycles.
May is showing an up-tick in the Sunspot count. This up and down, mostly down, will countinue for several years.
Note the change in the 30 Day Wolf Sunspot number–its about 50 now.
The final chart is a comparison of Solar Cycle 23 and Solar Cycle 24:
Solar irradiance was said to have dropped more than usual. It will have to fall off for months before it is likely to an event of consider “very interesting”.
All charts by Solen.info/solar
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.