No evidence for synchronization of the solar cycle by a "clock"

TL;DR

This study rigorously tests whether the solar cycle phases are synchronized by a precise clock or behave as a random walk, finding evidence against synchronization and supporting models with stochastic phase fluctuations.

Contribution

The paper provides the first comprehensive statistical analysis rejecting phase synchronization of the solar cycle, favoring randomly perturbed dynamo models.

Findings

Synchronization rejected at 95-99% significance levels.

Phases exhibit properties consistent with a random walk.

Supports models with little inter-cycle memory.

Abstract

The length of the solar activity cycle fluctuates considerably. The temporal evolution of the corresponding cycle phase, that is, the deviation of the epochs of activity minima or maxima from strict periodicity, provides relevant information concerning the physical mechanism underlying the cyclic magnetic activity. An underlying strictly periodic process (akin to a perfect "clock"), with the observer seeing a superposition of the perfect clock and a small random phase perturbation, leads to long-term phase stability in the observations. Such behavior would be expected if cycles were synchronized by tides caused by orbiting planets or by a hypothetical torsional oscillation in the solar radiative interior. Alternatively, in the absence of such synchronization, phase fluctuations accumulate and a random walk of the phase ensues, which is a typical property of randomly perturbed dynamo models. Based on the sunspot record and the reconstruction of solar cycles from cosmogenic C14, we carried out rigorous statistical tests in order to decipher whether there exists phase synchronization or random walk. Synchronization is rejected at significance levels of between 95% (28 cycles from sunspot data) and beyond 99% (84 cycles reconstructed from C14, while the existence of random walk in the phases is consistent with all data sets. This result strongly supports randomly perturbed dynamo models with little inter-cycle memory.