Progress in Solar Cycle Predictions: Sunspot Cycles 24–25 in Perspective Invited Review

• Published in: Solar physics Vol. 296; no. 3
• Main Author: Nandy, Dibyendu
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.03.2021
• Subjects: Astrophysics and Astroparticles; Atmospheric Sciences; Editors’ Choice; Invited Review; Physics; Physics and Astronomy; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Towards Future Research on Space Weather Drivers; Solar activity; Magnetohydrodynamics; Solar dynamo; Solar cycle prediction; Sunspots
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-021-01797-2

The dynamic activity of the Sun—sustained by a magnetohydrodynamic dynamo mechanism working in its interior—modulates the electromagnetic, particulate, and radiative environment in space. While solar activity variations on short timescale create space weather, slow long-term modulation forms the basis of space climate. Space weather impacts diverse space-reliant technologies while space climate influences planetary atmospheres and climate. Having prior knowledge of the Sun’s activity is important in these contexts. However, forecasting solar-stellar magnetic activity has remained an outstanding challenge. In this review, predictions for Sunspot Cycle 24 and the upcoming Solar Cycle 25 are summarized, and critically assessed. The analysis demonstrates that while predictions based on diverse techniques disagree across Solar Cycles 24–25, physics-based predictions for Solar Cycle 25 have converged and indicates a weak to moderate–weak sunspot cycle. I argue that this convergence in physics-based predictions is indicative of progress in the fundamental understanding of solar cycle predictability. Based on this understanding, resolutions to several outstanding questions related to solar cycle predictions are discussed; these questions include: is it possible to predict the solar cycle, what is the best proxy for predictions, how early can we predict the solar cycle and how many cycles into the future can we predict relying on our current understanding? Based on our analysis, we also suggest a rigorous pathway towards generating and disseminating a “consensus forecast” by any solar cycle prediction panels tasked with such a challenge.