Manifestations of the North – South Asymmetry in the Photosphere and in the Green Line Corona

Abstract

The north – south asymmetries (NSA) of three solar activity indices are derived and mutually compared over a period of more than five solar cycles (1945 – 2001). A catalogue of the hemispheric sunspot numbers, the data set of the coronal green line brightness developed by us, and the magnetic flux derived from the NSO/KP data (1975 – 2001) are treated separately within the discrete low- and mid-latitude zones (5° – 30°, 35° – 60°). The calculated autocorrelations, cross-correlations, and regressions between the long-term NSA data sets reveal regularities in the solar activity phenomenon. Namely, the appearance of a distinct quasi-biennial oscillation (QBO) is evident in all selected activity indices. Nevertheless, a smooth behavior of QBO is derived only when sufficient temporal averaging is performed over solar cycles. The variation in the significance and periodicity of QBO allows us to conclude that the QBO is not persistent over the whole solar cycle. A similarity in the photospheric and coronal manifestations of the NSA implies that their mutual relation will also show the QBO. A roughly two-year periodicity is actually obtained, but again only after significant averaging over solar cycles. The derived cross-correlations are in fact variable in degree of correlation as well as in changing periodicity. A clear and significant temporal shift of 1 – 2 months in the coronal manifestation of the magnetic flux asymmetry relative to the photospheric manifestation is revealed as a main property of their mutual correlation. This shift can be explained by the delayed large-scale coronal manifestation in responding to the emergence of the magnetic flux in the photosphere. The reliability of the derived results was confirmed by numerical tests performed by selecting different numerical values of the used parameters.