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Prediction of the strength and timing of sunspot cycle 25 reveal decadal-scale space environmental conditions - PubMed

  • ️Mon Jan 01 2018

Prediction of the strength and timing of sunspot cycle 25 reveal decadal-scale space environmental conditions

Prantika Bhowmik et al. Nat Commun. 2018.

Abstract

The Sun's activity cycle governs the radiation, particle and magnetic flux in the heliosphere creating hazardous space weather. Decadal-scale variations define space climate and force the Earth's atmosphere. However, predicting the solar cycle is challenging. Current understanding indicates a short window for prediction best achieved at previous cycle minima. Utilizing magnetic field evolution models for the Sun's surface and interior we perform the first century-scale, data-driven simulations of solar activity and present a scheme for extending the prediction window to a decade. Our ensemble forecast indicates cycle 25 would be similar or slightly stronger than the current cycle and peak around 2024. Sunspot cycle 25 may thus reverse the substantial weakening trend in solar activity which has led to speculation of an imminent Maunder-like grand minimum and cooling global climate. Our simulations demonstrate fluctuation in the tilt angle distribution of sunspots is the dominant mechanism responsible for solar cycle variability.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1

Simulated butterfly diagram of the solar cycle. Century-scale simulation of solar surface magnetic field evolution covering sunspot cycle 15 to the currently on-going cycle 24. The butterfly diagram depicts the spatio-temporal variation of the longitudinally averaged radial magnetic field (in gauss) on the Sun’s surface

Fig. 2
Fig. 2

Data-driven simulation of solar surface polar flux. a This panel depicts the evolution of the total unsigned flux associated with sunspots which is used to drive the surface flux transport model until September 2016 (epoch marked by the dashed vertical line). The gray and solid black curves represent monthly and annually averaged unsigned flux, respectively. The blue and set of green curves beyond September 2016 depicts different realizations of the modeled descending phase of cycle 24 used as synthetic inputs to forward run the surface flux transport model. b Time evolution of polar flux calculated from our surface flux transport simulation is compared with those obtained from polar faculae observations. The light blue (and light red) curve with error bars represents the polar flux estimated from polar faculae observations in the northern (and the southern) hemisphere, whereas the solid blue (and red) curve shows the polar flux obtained from our simulation for corresponding hemispheres. The dashed blue (and dashed red) curve beyond 2014.5 represents the polar flux obtained from WSO polar field observations for the northern (and the southern) hemisphere. The set of light and dark cyan and magenta curves beyond September 2016 (vertical dashed line) depict predicted polar fluxes (up to 2020) from ensemble runs with varying input fluxes and tilt angle fluctuations, respectively. The black and dark red curves represent the polar field prediction from our standard run

Fig. 3
Fig. 3

Dynamo simulations of the Sun’s internal magnetic field driven by surface inputs. a Solar surface flux transport model prediction of the Sun’s surface magnetic field distribution near cycle 24 minimum. b Left: The poloidal field distribution within the Sun’s convection zone in the internal dynamo model following assimilation of the data from the surface flux transport model. b Right: The dynamo model predicted toroidal field within the Sun’s convection zone during cycle 25 maximum

Fig. 4
Fig. 4

Prediction of sunspot cycle 25. Solar dynamo simulated sunspot cycles (magenta curve) compared with the observed sunspot cycle (unsigned magnetic flux; black curve), where both quantities are yearly averaged. The light gray curve in the background represents monthly averaged unsigned sunspot flux. The blue and set of green curves between the vertical black dashed and solid lines depict flux associated with the thirty-four synthetic profiles used in the surface flux transport model as plausible realizations of the descending phase of cycle 24. The magenta curve beyond the solid-black vertical line (corresponding to our standard simulation) depicts the predicted shape and strength of sunspot cycle 25. The set of two black curves beyond the solid-black vertical line represent the strongest and the weakest magnetic cycles (that is the range of our ensemble forecast) based on our diverse predictive dynamo runs. The prediction range (uncertainty) indicates cycle 25 will be similar or slightly stronger than the previous cycle

Fig. 5
Fig. 5

Vector potential on the solar surface obtained from solar surface flux transport and dynamo simulations at the beginning of cycle 17. a Depicts a comparison between ASFT(R⊙,θ)sinθ and ADyn(R⊙,θ)sinθ. b Depicts the associated γ(θ)

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