  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
$\pm10^\circ$ latitude from the solar equator.
