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2010 ; 7
(ä): 6
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Solar Cycle Prediction
#MMPMID27194963
Petrovay K
Living Rev Sol Phys
2010[]; 7
(ä): 6
PMID27194963
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A review of solar cycle prediction methods and their performance is given,
including forecasts for cycle 24. 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. Their
implicit assumption 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. Finally, instead of an analysis
of observational data alone, model based predictions use physically (more or
less) consistent dynamo models in their attempts to predict solar activity. In
their overall performance during the course of the last few solar cycles,
precursor methods have clearly been superior to extrapolation methods.
Nevertheless, most precursor methods overpredicted cycle 23, while some
extrapolation methods may still be worth further study. Model based forecasts
have not yet had a chance to prove their skills. One method that has yielded
predictions consistently in the right range during the past few solar cycles is
that of K. Schatten et al., whose approach is mainly based on the polar field
precursor. The incipient cycle 24 will probably mark the end of the Modern
Maximum, with the Sun switching to a state of less strong activity. It will
therefore be an important testbed for cycle prediction methods and, by inference,
for our understanding of the solar dynamo.
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