THE CAUSE OF THE WEAK SOLAR CYCLE 24

The ongoing 11 year cycle of solar activity is considerably less vigorous than the three cycles before. It was preceded by a very deep activity minimum with a low polar magnetic flux, the source of the toroidal field responsible for solar magnetic activity in the subsequent cycle. Simulation of the evolution of the solar surface field shows that the weak polar fields and thus the weakness of the present cycle 24 are mainly caused by a number of bigger bipolar regions emerging at low latitudes with a wrong (i.e., opposite to the majority for this cycle) orientation of their magnetic polarities in the north-south direction, which impaired the growth of the polar field. These regions had a particularly strong effect since they emerged within +/- 10 degrees latitude from the solar equator.