Long-term changes in the north–south asymmetry of solar activity: a nonlinear dynamics characterization using visibility graphs

Y Zou,J Kurths,M Small,R V Donner,N Marwan

doi:10.5194/npg-21-1113-2014

Abstract

Abstract. Solar activity is characterized by complex dynamics superimposed onto an almost periodic, approximately 11-year cycle. One of its main features is the presence of a marked, time-varying hemispheric asymmetry, the deeper reasons for which have not yet been completely uncovered. Traditionally, this asymmetry has been studied by considering amplitude and phase differences. Here, we use visibility graphs, a novel tool of nonlinear time series analysis, to obtain complementary information on hemispheric asymmetries in dynamical properties. Our analysis provides deep insights into the potential and limitations of this method, revealing a complex interplay between factors relating to statistical and dynamical properties, i.e., effects due to the probability distribution and the regularity of observed fluctuations. We demonstrate that temporal changes in the hemispheric predominance of the graph properties lag those directly associated with the total hemispheric sunspot areas. Our findings open a new dynamical perspective on studying the north–south sunspot asymmetry, which is to be further explored in future work.

Highlights

Starting with the pioneering works of Schuster (1898) and Yule (1927), long-term variations in solar activity have been among the most studied examples of complex variability patterns in nature for more than a century, and their past presence has been shown in many paleo-archives (Bond et al, 2001; Agnihotri et al, 2002)
Related to the non-negativity of the studied sunspot areas, the considered time series exhibit strongly non-Gaussian probability distribution functions (PDFs, see Fig. 4a, b), which can change themselves with time due to the complex dynamics of the solar activity cycle
Beyond the results on long-term variations in nonlinear dynamics characteristics provided in this study, we suggest that a combination of information on amplitude and phase relationships with additional results on dynamic complexity has great potential for opening a new view on the north–south asymmetry of solar activity, its temporal organization and dynamics and, its potential causes and underlying physical mechanisms

Summary

Introduction

Starting with the pioneering works of Schuster (1898) and Yule (1927), long-term variations in solar activity have been among the most studied examples of complex variability patterns in nature for more than a century, and their past presence has been shown in many paleo-archives (Bond et al, 2001; Agnihotri et al, 2002). Variations in solar activity are known to have considerable influence on Earth system dynamics at various timescales. Knowledge of solar activity is important to understand past climate variations (Bard and Frank, 2006). The two aforementioned examples illustrate the importance of anticipating both short- and long-term behavior of solar activity (Kurths and Ruzmaikin, 1990; Brajša et al, 2009; Petrovay, 2010)

Results

Discussion

Conclusion