PERIODICITIES IN THE SOLAR DIFFERENTIAL ROTATION, SURFACE MAGNETIC-FIELD AND PLANETARY CONFIGURATIONS

Using Greenwich data on sunspot groups during 1874-1976, we have studied the temporal variations in the differential rotation parameters A and B by determining their values during moving time intervals of lengths 1-5 yr successively displaced by 1 yr. FFT analysis of the temporal variations of B (or B/A) shows periodicities 18.3 +/- 3 yr, 8.5 +/- 1 yr, 3.9 +/- 0.5 yr, 3.1 +/- 0.2 yr, and 2.6 +/- 0.2 yr at levels greater than or equal to 2 sigma. This analysis also shows five more periodicities at levels 1-2 sigma. The maximum entropy method is used to set narrower limits on the values of these periods. The reality of the existence of all these periodicities of B (or B/A) except the one at 2.8 yr is confirmed by analyzing the simulated time series of B and B/A with values of A and B randomly distributed within the limits of their respective uncertainties. Four of the prominent periods of B agree, within their uncertainties, with the known periods in the the large-scale photospheric magnetic field. The deviations from the average differential rotation are larger near the sunspot minima. On longer time scales, the variations in the amount of sunspot activity per unit time are well correlated to the variations in the amplitudes of the 'torsional oscillation' represented by the 22-yr periodicity in B. All the periods in B found here are in good agreement with the synodic periods of two or more consecutive planets. The possibility of planetary configurations providing perturbations needed for the Sun's MHD torsional oscillations is speculated upon and briefly discussed.