Solar cycle prediction

Abstract

A review of solar cycle prediction methods and their performance is given, including early forecasts for Cycle 25. The review focuses on those aspects of the solar cycle prediction problem that have a bearing on dynamo theory. The scope of the review is further restricted to the issue of predicting the amplitude (and optionally the epoch) of an upcoming solar maximum no later than right after the start of the given cycle. Prediction methods form three main groups. Precursor methods rely on the value of some measure of solar activity or magnetism at a specified time to predict the amplitude of the following solar maximum. The choice of a good precursor often implies considerable physical insight: indeed, it has become increasingly clear that the transition from purely empirical precursors to model-based methods is continuous. Model-based approaches can be further divided into two groups: predictions based on surface flux transport models and on consistent dynamo models. The implicit assumption of precursor methods is that each numbered solar cycle is a consistent unit in itself, while solar activity seems to consist of a series of much less tightly intercorrelated individual cycles. Extrapolation methods, in contrast, are based on the premise that the physical process giving rise to the sunspot number record is statistically homogeneous, i.e., the mathematical regularities underlying its variations are the same at any point of time, and therefore it lends itself to analysis and forecasting by time series methods. In their overall performance during the course of the last few solar cycles, precursor methods have clearly been superior to extrapolation methods. One method that has This article is a revised version of

Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude

“…We have strong reservations about the latter given the discussion above on the overlapping nature of Hale cycles, their impact on the sunspot cycle (M2014), and especially in the context of solar-minimum conditions that result from the mutual cancellation of four magnetic bands-not to mention the subjectivity of picking when sunspot minimum occurs (e.g. Petrovay, 2020).…”

“…In recent decades, as the amplitude and timing of the sunspot cycle has reached greater societal significance, community-wide panels have been convened and charged with constructing consensus opinions on the upcoming sunspot cycle-several years in advance of the upcoming peak (Pesnell, 2008). Lack of adequate constraints, conflicting assumptions related to the solar dynamo mechanism, and different techniques, safe to say, result in a broad range of submissions to these panels that cover almost all potential "physically reasonable" outcomes (Pesnell, 2016;Petrovay, 2020).…”

“…Sunspot cycle prediction is a high-stakes business and has become a decadal event, starting officially for Solar Cycle 23 (Joselyn et al, 1997), and repeated for Solar Cycle 24 (Pesnell, 2008), the effort brought together a range of subject matter experts and an array of submitted methods that range from polar magnetic field precursors, through numerical models, and also using observed climatologies to extrapolate in time (e.g. Petrovay, 2020). It is worth noting that the 'polar field precursor' method, which uses measurements of the Sun's polar magnetic field at solar minimum to predict the upcoming sunspot cycle strength, proved to be accurate for Solar Cycle 24 (e.g.…”

An ACE/CRIS-observation-based Galactic Cosmic Rays heavy nuclei spectra model II

“…The accuracy of predicting the upcoming GCR environment depends in part then on the forecast of the SSN, but that is not the core issue of this paper. Many techniques and methods have been proposed to forecast the SSN over the years [49][50][51]. Here, we illustrate the applicability of our GCR model and use it to derive a predictable GCR environment for the readers.…”

Towards an algebraic method of solar cycle prediction

“…where B is the azimuthal average of the large scale photospheric magnetic field (assumed to be radial) while k is heliographic latitude. The value D n of this dipole moment at the start of cycle n is widely considered the best physics-based precursor of the the amplitude of the incipient cyle n (Petrovay, 2020). Understanding intercycle variations in solar activity and potentially extending the scope of the prediction calls for an effective and robust method to compute D n from (often limited) observational data on the previous course of solar activity.…”