On The Question of North–South Asymmetry of Solar Activity

Abstract

The paper studies the dynamics of the distribution of the index of the north–south asymmetry of the sunspot number for the phase of the 11-year cycle, from cycle to cycle, for the period 1874–2012. The used method of expansion over natural orthogonal functions makes it possible to estimate the contribution of different harmonics. It is shown that the contribution of the first harmonic of the decomposition varies from cycle to cycle from 25 to 45% and that the contribution of the first three harmonics is more than 70%. The correlation coefficient for the annual values of the north–south asymmetry of the sunspot number in the cycle and the corresponding values of the first time component of the decomposition varies from cycle to cycle, from 0.9 or higher. It is shown that the north–south asymmetry of the sunspot number is determined mainly by the periodic shift of the cyclic curves of the northern and southern hemispheres relative to each other. This ensures the appearance in the spectrum of 11-, 40-, and 80-year variations in the index of the north–south asymmetry of harmonics.