Periodicity of North–South asymmetry of sunspot area revisited: Cepstrum analysis

The North–South asymmetry in solar activity is an important solar property. During recent years the presence of short and intermediate-term periodicities of the North–South asymmetry has been reported, implying it could be an observational constraint that should be explained by the solar dynamo action. We attempt to confirm reported periodicities by employing an independent method so that observational constraints are established. We adopt the cepstrum technique to deconvolve the signal and the noise so that spurious peaks due to random noise are eliminated in the Fourier power spectrum. We also demonstrate how effectively it removes random noise using artificial data generated by assuming that the asymmetry of the sunspot area is characterized by random noise superposed on a slowly varying sinusoidal background function. We find that (i) the main periodicity of the North–South difference corresponding to ∼9 years is present, (ii) other periodicities recently claimed, such as, of ∼1.4, ∼3.8, ∼43 years, can not survive the deconvolution process, suggesting they seem due to stochastic random noise. We conclude by pointing out a possible implication of our finding on the nature of the North–South asymmetry of solar activity.