Grand minima and maxima of solar activity: New observational constraints
Ilya Usoskin Submitted: 2007-06-04 00:54
Using a reconstruction of sunspot numbers stretching over multiple millennia,
we analyze the statistics of the occurrence of grand minima and maxima
and set new observational constraints on long-term solar and stellar dynamo models.
We present an updated reconstruction of sunspot number over multiple millennia,
from 14C data by means of a physics-based model, using an updated model of the evolution of
the solar open magnetic flux.
A list of grand minima and maxima of solar activity is presented for
the Holocene (since 9500 BC) and the statistics of both the length of individual
events as well as the waiting time between them are analyzed.
The occurrence of grand minima/maxima is driven not by long-term cyclic
variability, but by a stochastic/chaotic process.
The waiting time distribution of the occurrence of grand minima/maxima deviates from
an exponential distribution, implying that these events tend to cluster
together with long event-free periods between the clusters.
Two different types of grand minima are observed: short (30-90 years) minima of Maunder
type and long (>110 years) minima of Sp''orer type, implying that a
deterministic behaviour of the dynamo during a grand minimum defines its length.
The duration of grand maxima follows an exponential distribution, suggesting
that the duration of a grand maximum is determined by a random process.
These results set new observational constraints upon the long-term
behaviour of the solar dynamo.
Authors: I.G. Usoskin, S.K. Solanki, G.A. Kovaltsov
Publication Status: A&A accepted
Last Modified: 2007-06-04 23:59