by Frank Bosse and Fritz Vahrenholt
(Translated/edited by P Gosselin)
The central star of our solar system was quite inactive last month. The measured solar sunspot number (SSN) was 57.7. That is only 79% of what is the average for this time point into a solar cycle compared to the mean of the 23 previous complete cycles. What follows is a comparison:
Figure 1: The current solar cycle 24 (red) in relation to the mean of all the other previous 23 solar cycles (blue), and to the very similar solar cycle no. 5, which ended in 1810.
For the complete years of the current cycle, a plot of the activity percentage with respect to the mean appears as follows:
Figure 2: Relative sunspot activity of each calendar year for solar cycle no. 24.
For the entire solar cycle so far (now 7 years and 1 month) the sun’s activity has reached only 56% of the mean solar cycle. The deviation from the mean for the accumulated sunspots of the individual cycles 7 years and one month into the cycle are plotted as follows:
Figure 3: The accumulated solar sunspot anomalies from the mean cycle (blue in Figure 1) for each cycle, 7 years and one month into the cycle.
It is clear to see that the phase between solar cycle no. 17 (started in 1933) and the end of solar cycle no. 23 in 2008 was the most active since systematic observations began. That phase was abruptly ended by the current cycle.