Periodicities in the North–south Asymmetry of the Solar Differential Rotation and Surface Magnetic Field

ISSN： 0038-0938

Source： Solar Physics, Vol.170, Iss.2, 1997-02, pp. : 389-410

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Abstract

We have studied the temporal variations in the north–south asymmetries of the differential rotation parameters A, B, and the `mean' rotation rate overline{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 (overline{A}a) of overline{A}is similar to the variation in the asymmetry (Ba) of Bbut with opposite sign. These variations of overline{A}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, overline{A}a, and the north–south asymmetry (Aa) of A, show existence of significant periodicities: 45.5 pm 11.5 yr, 21.3 pm 4.5 yr, 13.3 pm 1.5 yr, and 10.5 pm 0.5 yr. These analyses also show a few other possible periodicities in Aa, Ba, and overline{A}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.