PERIODICITIES IN THE NORTH–SOUTH ASYMMETRY OF THE SOLAR DIFFERENTIAL ROTATION AND SURFACE MAGNETIC FIELD

Abstract

We have studied the temporal variations in the north–south asymmetries of the differential rotation parameters A, B, and the ‘mean’ rotation rate Ā, 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 (Ā $a$) of Ā is similar to the variation in the asymmetry (B $a$) of B but with opposite sign. These variations of Ā$a$ and B $a$ 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 $a$ , Ā $a$ , and the north–south asymmetry (A $a$ ) 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 $a$ , B $a$ , and Ā$a$ . 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.