Has SC24-maximum passed?
posted: Nov 10, 2012

Once again, last week's activity was not particularly exciting: Just a few small single sunspots, that was it! Also, the SIDC announced that the provisional sunspot number for October was 53.3. That is the lowest since February this year. What a difference with the sunspot activity one year ago: Several groups dotted the solar surface during that November month, and also the biggest sunspot group so far this solar cycle (NOAA 1339) made its appearance. Obviously, one wonders if SC24-maximum has already passed.

Though the smoothed International Sunspot Number (ISN) shows a maximum late 2011, chances are very low that this is the true maximum of SC24. There are several reasons to come to this conclusion. For example, a maximum late 2011 would mean that the time of rise (i.e. the time needed for a solar cycle to rise from its minimum to its maximum) would only be about 3 years. Such short rise times are usually reserved for very active and short cycles such as SC22 which only needed 37 months to reach its maximum sunspot number of about 160 in October 1989. In contrast, lower amplitude cycles like SC20 in 1969 and SC23 in 2000 needed already more than 4 years to reach their resp. maximum.

One can also see that last year's "maximum" was mainly due to activity on the northern solar hemisphere, which produced most of the big groups and strong flares. Since then, northern activity has subsided somewhat, while that on the southern hemisphere has gradually been increasing. It is reasonable to expect that when the southern sunspot maximum peaks, a new and higher sunspot maximum will occur, and that this might be the true SC24-maximum.

Low amplitude sunspot cycles are also known for a broad maximum with several ups-and-downs. Graph underneath compares the smoothed monthly sunspot number of the ongoing solar cycle with that of SC16. Clearly, one can see that a solar cycle can have multiple maxima, and that the first sunspot peak does not necessarily have to be the highest.

The average latitude at which the sunspot groups appear, is currently also very normal indicating that the true maximum is still to come. The groups on the northern hemisphere appear on the average a few degrees closer to the solar equator than on the southern, consistent with the higher activity that took place on the northern hemisphere late 2011.
All the above arguments are of course only indirect indications for a maximum that has not happened yet. Moreover, solar observers are well aware that the Sun isn't shy of pulling a new trick out of her sleeve. Nonetheless, a SC24-maximum that is yet to come (2013 - see SIDC-prediction charts) is at the moment a lot more likely than the claim that the maximum took already place (late 2011).