Abstract:
We have studied the temporal variations in the north–south asymmetries of the differential rotation parameters A, B, and the mean rotation rate , 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 a) of is similar to the variation in the asymmetry (B ) of B but with opposite sign. These variations of and B 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 B , , and the north–south asymmetry (A ) 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 ± 0.5 yr. These analyses also show a few other possible periodicities in A , B , and . 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.
