The long way to solar maximum

Everybody has noticed it: Over the last few months, solar activity has shifted into a higher gear.

Since October last year, more and bigger sunspot groups have appeared on the solar disk, gradually driving the monthly sunspot number to new heights. Indeed, in February, preliminary values (SILSO) for the international sunspot number reached 102.8, the highest so far this solar cycle. Also the smoothed sunspot number is on the rise and easily surpasses the previous "maximum" that occurred late 2011-early 2012. Five years after its start in December 2008, Solar Cycle 24 (SC24) seems finally to have arrived at its maximum.

This upswing in solar activity is also noticeable in other parameters, such as the radio-flux or the number of solar flares. As can be seen in the chart underneath (data from NOAA/NGDC), the number of medium (M) and extreme (X) flares has been at a relatively high level. So far this solar cycle, there have been 8 months with more than 20 M- and X-class flares, and half of those have occurred over the last 5 months. Over the same time period, one third of all M/X-flares in SC24 were produced.

This ongoing maximum of SC24 seems to be on the account of the southern hemisphere, contrary to the 2011-2012 bump which happened mostly on the northern hemisphere. These timings are in line with the onset of solar activity as well as with the reversals of the polar magnetic fields of the Sun (see this STCE news item). Double peaked maxima are by no means exceptional, they happened for example also during the previous 2 solar cycles. Nonetheless, cycles with lower amplitudes such as SC24 have a longer and more complex maximum phase, quite different from a "classical" single or double sharp peak. These are actual manifestations of the solar dynamo, which are not encompassed by most solar cycle models which only show a smooth, asymmetric cycle shape.

Pending the further evolution of the solar activity, the (smoothed) maximum is expected to occur late 2013 or in 2014. That means the time of rise would be around 5 years, which is relatively long compared to the "average" solar cycle. However, as the maximum is forecast to be relatively low too, these timings are perfectly similar to previous solar cycles with comparable amplitude (e.g. SC12). It is also possible that another "bump" occurs during the declining phase of the solar cycle, as has been observed in various other solar cycles such as SC17. It is clear we're not done yet with this solar cycle!

Credits - Sunspot data are available at SILSO, and the flare data at NOAA/NGDC.

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