Gradual onset of the Maunder Minimum revealed by high-precision carbon-14 analyses

Hiroko Miyahara,Kazuho Horiuchi,Fuyuki Tokanai,Hideyuki Hotta,Mirei Takeyama,Hirohisa Sakurai,Toru Moriya

doi:10.1038/s41598-021-84830-5

Hiroko Miyahara, Kazuho Horiuchi + Show 5 more

Open Access

https://doi.org/10.1038/s41598-021-84830-5

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Abstract

The Sun exhibits centennial-scale activity variations and sometimes encounters grand solar minimum when solar activity becomes extremely weak and sunspots disappear for several decades. Such an extreme weakening of solar activity could cause severe climate, causing massive reductions in crop yields in some regions. During the past decade, the Sun’s activity has tended to decline, raising concerns that the Sun might be heading for the next grand minimum. However, we still have an underdeveloped understanding of solar dynamo mechanisms and hence precise prediction of near-future solar activity is not attained. Here we show that the 11-year solar cycles were significantly lengthened before the onset of the Maunder Minimum (1645–1715 CE) based on unprecedentedly high-precision data of carbon-14 content in tree rings. It implies that flow speed in the convection zone is an essential parameter to determine long-term solar activity variations. We find that a 16 year-long cycle had occurred three solar cycles before the onset of prolonged sunspot disappearance, suggesting a longer-than-expected preparatory period for the grand minimum. As the Sun has shown a tendency of cycle lengthening since Solar Cycle 23 (1996–2008 CE), the behavior of Solar Cycle 25 can be critically important to the later solar activity.

Highlights

The Sun shows long-term variations with scales ranging from several decades to a few millennia[1, 2] in addition to the basic decadal-scale cycle, and sometimes brings deep minima in its activity, lasting for several decades or even more than a century[3]
It is well known that the polar magnetic field in the solar cycle minimum highly correlates with the sunspot number in the solar m aximum[10]
Replicated measurements of tree-ring carbon-14 concentrations were conducted using the compact Accelerator Mass Spectrometer installed at Yamagata University in Japan[26, 27]

Summary

Introduction

The Sun shows long-term variations with scales ranging from several decades to a few millennia[1, 2] in addition to the basic decadal-scale cycle, and sometimes brings deep minima in its activity, lasting for several decades or even more than a century[3]. The galactic cosmic rays shielded by the solar and heliospheric magnetic field produce carbon-14 or beryllium-10; their production rates reflect the variations of solar activity. It is well known that the polar magnetic field in the solar cycle minimum highly correlates with the sunspot number in the solar m aximum[10]. We can predict the polar magnetic field on the basis of the observed sunspot pairs even before the solar minimum by using the surface flux transport model. Some studies suggest that the lengthening of the 11-year cycle is related to the speed of meridional circulation in the solar convection zone[17, 18] that could affect the efficiency of the transport or diffusion of the solar magnetic field, their relationship is unverified

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