Prediction of the strength and timing of sunspot cycle 25 reveal decadal-scale space environmental conditions (1909.04537v1)

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.

• The paper presents ensemble forecasting with century-scale simulations that predict cycle 25 to be similar or slightly stronger than cycle 24.
• It employs a coupled surface flux transport and dynamo model to simulate solar magnetic field dynamics over the past century.
• The study reveals tilt angle fluctuations as a key mechanism driving solar variability, reinforcing the Babcock-Leighton framework.

Prediction of the Strength and Timing of Sunspot Cycle 25: A Comprehensive Assessment

The paper "Prediction of the Strength and Timing of Sunspot Cycle 25 Reveal Decadal-scale Space Environmental Conditions," authored by Prantika Bhowmik and Dibyendu Nandy, presents an advanced methodological approach for predicting solar activity. Utilizing an overview of magnetic field evolution models, the paper not only extends the prediction window of sunspot cycles to nearly a decade but also provides insights into the mechanisms governing solar variability.

The paper focuses on the prediction of sunspot cycle 25, employing a combination of data-driven simulations and theoretical models. Specifically, it integrates a solar surface flux transport (SFT) model with a solar dynamo model to simulate solar activity over the past century and to forecast future trends. This approach is predicated on the idea that understanding and simulating the solar polar field dynamics during cycle minima can facilitate accurate predictions of the subsequent cycle's properties.

Key Contributions and Findings

1. Century-Scale Simulation: The paper utilizes century-scale, data-driven simulations, capturing solar magnetic field dynamics from 1913 onwards. This long-term approach is crucial for understanding the historical variability of solar cycles.
2. Ensemble Forecasting: By generating multiple runs with variations in key parameters such as tilt angle and sunspot input profiles, the authors manage to account for uncertainties and generate a range of possible outcomes for cycle 25.
3. Mechanism of Variability: The research pinpoints fluctuations in the tilt angle distribution of sunspots as the predominant mechanism influencing solar cycle variability. This finding supports the Babcock-Leighton framework for solar dynamo theory, emphasizing the surface processes in the amplification of the solar magnetic field.
4. Prediction Outcome: The ensemble forecast predicts that sunspot cycle 25 will be similar to or slightly stronger than cycle 24. Thereby, it refutes extreme scenarios of a further decline to a possible Maunder-like grand minimum.
5. Implications for Space Weather: The predicted strength and time of peak activity, around 2024, provides critical information for anticipating and mitigating the impact of space weather on global technological systems.

Methodological Approach

The authors employ a two-step modeling process:

• Surface Flux Transport (SFT) Model: This model simulates the evolution of the Sun's photospheric magnetic field. It relies on historical sunspot records and magnetic flux transport dynamics to simulate changes over time.
• Dynamo Model: An internal solar dynamo model, driven by SFT model outputs, calculates the conversion of poloidal to toroidal magnetic fields within the Sun's convection zone. This process is crucial for predicting the amplitude of future sunspot cycles.

Theoretical and Practical Implications

From a theoretical standpoint, the successful implementation of an extended prediction model underscores the importance of integrating surface and internal solar processes. This suggests a robust validation of the Babcock-Leighton mechanism as a dominant process in generating solar magnetic fields. Practically, the predictions inform stakeholders involved in space weather forecasting and related technological sectors. These insights serve as valuable references for global climate models that incorporate solar radiative forcing.

Future Directions

The findings suggest several promising directions for future research. Continued refinement of the prediction model, incorporating more real-time observational data, could enhance forecast accuracy further. Additionally, exploring the model's sensitivity to various turbulence parameters within the solar convection zone could offer deeper insights into the fundamental processes governing solar activity. Expanding the model to include interstellar magnetic interactions might also provide a more comprehensive picture of space weather impacts.

Conclusion: The research by Bhowmik and Nandy marks a significant step in solar cycle prediction, offering a more detailed and reliable framework for forecasting solar activities. These advances align with the long-term goals of improving space weather preparedness and understanding the broader implications of solar dynamics on Earth's climate system.