Solar Cycle 24 has had the lowest solar activity since the Dalton Minimum around 1810.
Our sun was also very sub-normally active in December last year. We are writing the 121st month since the beginning of cycle number 24, in December 2008, and since 2012 (when we started the blog here) we could only reformulate the opening sentence once: In September 2017 when the sun was 13% more active than the long-term (since 1755) average.
All other months were below average. With the sunspot number (SSN) of 3.1 for the monthly average for December and a total of 24 days without any spot (throughout the second half of the month the sun was spotless) we are in the middle of the cycle minimum.
Fig. 1: Solar Cycle 24 – red – is almost over. Since October 2017 (cycle month 108) we have been at the minimum and the next cycle should start at the beginning of 2020. The blue curve is the respective monthly average over the 23 cycles completed so far. The black curve (for comparison) SC 5, which was recorded around 1815 and was as similarly weak as the current cycle.
The following chart compares all the cycles observed thus far:
Fig. 2: The sunspot activity of our sun since cycle 1 (1755). The numbers are calculated by adding the monthly differences with respect to the mean (blue in Fig.1) up to the current cycle month 121.
Clearly SC 24 is the lowest activity since the Dalton Minimum (SC 5,6,7) around 1810 when using the entire cycle and not only the maximum activity in short peaks (see Fig. 1).