Periodicities in the north - south asymmetry of the solar differential rotation and surface magnetic field

We have studied the temporal variations in the north - south asymmetries of the differential parameters A, B, and the 'mean' rotation rate A, by determining their values from Greenwich data for sunspot groups (1879-1976) in the northern and southern hemispheres, during moving time intervals of lengths 3 yr and 5 yr, successively displaced by 1 yr. The variation in the north - south asymmetry (<(A)over bar a>) of (A) over bar is similar to the variation in the asymmetry (Ba) of B but with opposite sign. These variations of <(A)over bar a> and Ba may represent components of an anti-symmetric torsional oscillation which are in opposite phase with each other. The FFT and MEM analyses of the temporal variations of Ba, Aa, and the north - south asymmetry (Aa) of A, show existence of significant periodicities: 45.5+/-11.5 yr, 21.3+/-4.5 yr, 13.3+/-1.5 yr, and 10.5 i 0.5 yr. These analyses also show a few other possible periodicities in Aa, Ba, and (A) over bar A. All these periodicities are also seen in the north - south asymmetry of sunspot activity (with similar relative magnitudes). The 22-yr periodicity was seen in 'even-parity' modes of magnetic field inferred from sunspot data.