IS THE SOLAR-CYCLE TIMED BY A CLOCK

Dicke (1978) has argued that the phase of the solar cycle appears to b e coupled to an internal clock: shorter cycles are usually followed by longer ones, as if the Sun remembers the correct phase. The data set is really too short to demonstrate the presence of a phase memory, but phase and amplitude of the cycle are strongly correlated for 300 yr o r more. It is shown that this memory effect can be explained by mean f ield theory in terms of fluctuations in alpha, which induce coherent c hanges in the frequency and amplitude of a dynamo wave. It is conclude d that there is neither a strong observational indication nor a theore tical need for an extra timing device, in addition to the one provided by dynamo wave physics.