  The solar magnetic activity cycle causes changes in the Sun on timescales
that are relevant to human lifetimes. The minimum in solar activity that
preceded the current solar cycle (cycle 24) was deeper and quieter than any
other recent minimum. Using data from the Birmingham Solar-Oscillations Network
(BiSON), we show that the structure of the solar sub-surface layers during the
descending phase of the preceding cycle (cycle 23) was very different from that
during cycle 22. This leads us to believe that a detailed examination of the
data would have led to the prediction that the cycle-24 minimum would be out of
the ordinary. The behavior of the oscillation frequencies allows us to infer
that changes in the Sun that affected the oscillation frequencies in cycle 23
were localized mainly to layers above about 0.996Rsun, depths shallower than
about 3000 km. In cycle 22, on the other hand, the changes must have also
occurred in the deeper-lying layers.
