Magnetically Preferred Solar Longitudes: Reality?

The observed persistence of specific periodicities detected in time series associated with solar surface magnetic activity over several solar cycles has led to numerous papers supporting the existence of preferred longitudes. Recent analysis of the past 120 years of sunspot number data showed that no observed periodicity remained coherent for durations greater than two 11-year solar cycles. Here we address the question: Could the observed periodicities of solar magnetic signals on time scales of two decades be the result of a purely stochastic process? We begin to answer this by comparing phase coherence between observed periodic signals and signals from a model using longitudinally random eruptions. A surprisingly non-negligible likelihood is found, approximately 1 in 3, that observed periodicities from integrated full-disk solar parameters are a chance occurrence for time series on the order of 20 years in duration.