This year was supposed to be the year of maximum solar activity, the peak of the 11-year sunspot cycle.. Already this month is March and still the solar activity is low. Sunspot numbers are well below their values from 2011, and strong solar flares have been infrequent
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| Monthly sunspot numbers for solar cycle 24 (the current one), cycle 23, and cycle 21, the last one with one, normal peak. |
Reality is more complicated. Astronomers have been counting sunspots for centuries, and they have seen that the solar cycle is not perfectly regular. The back-and-forth swing in sunspot counts can take anywhere from 10 to 13 years to complete. Also, the amplitude of the cycle varies; some solar maxima are very weak, others very strong.
Pesnell notes yet another complication in the solar cycle: “The last two solar maxima, around 1989 and 2001, had not one but two peaks.” Solar activity went up, dipped, then rose again, performing a mini-cycle that lasted about two years. The same thing could be happening now, as sunspot counts jumped in 2011 and dipped in 2012. Pesnell expects them to rebound in 2013: “I am comfortable in saying that another peak will happen in 2013 and possibly last into 2014,”
NASA images courtesy Solar Dynamics Observatory and Helioseismic and Magnetic Imager science teams. Sunspot number data from the NOAA National Geophysical Data Center. NASA animation by Robert Simmon. Caption adapted from a story by Tony Phillips, Science@NASA.
- Instrument:
- SDO - HMI