Wavelet analysis of temporal fluctuations of the solar polar magnetic field

Abstract We study temporal fluctuations of the solar polar magnetic field using wavelet analysis applied to observational data obtained at Wilcox Solar Observatory since May 1976 thus covering four and a half solar cycles. The wavelet approach allows us to construct smooth spectra over a wide range of temporal scales, and to study scale-by-scale correlations and non-stationary properties of the signal. The spectra of the polar field fluctuations show a continuous power-law behavior over a broad range of scales. In the intermediate range, the spectral slope is close to −5/3, while at longer time scales the spectrum becomes steeper, approaching values close to −7/3 for the symmetric component. The spectral energy of the fluctuations is found to increase during maximum sunspot activity with the strongest enhancement occurring during the polarity-reversal phase as the polar field approaches zero. Filtered oscillations at periods of about 3.5 years show intervals of phase synchronization between the northern and southern hemispheres interrupted by phase disturbances. The obtained results indicate that the variability of the large-scale solar magnetic field contains a significant broadband fluctuating component, possibly associated with turbulent and nonlinear processes in the solar dynamo.