Extreme solar events (2205.09265v1)

Abstract: We trace the evolution of research on extreme solar and solar-terrestrial events from the 1859 Carrington event to the rapid development of the last twenty years. Our focus is on the largest observed/inferred/theoretical cases of sunspot groups, flares on the Sun and Sun-like stars, coronal mass ejections, solar proton events, and geomagnetic storms. The reviewed studies are based on modern observations, historical or long-term data including the auroral and cosmogenic radionuclide record, and Kepler observations of Sun-like stars. We compile a table of 100- and 1000-year events based on occurrence frequency distributions for the space weather phenomena listed above. Questions considered include the Sun-like nature of superflare stars and the existence of impactful but unpredictable solar "black swans" and extreme "dragon king" solar phenomena that can involve different physics from that operating in events which are merely large.

• The paper provides a comprehensive review of historical and modern solar observations, establishing statistical limits for extreme solar phenomena.
• It employs detailed analyses of sunspot groups, flares, and CMEs to estimate potential 100- and 1000-year event magnitudes.
• The study highlights the implications for space weather resilience and directs future research toward improved predictive models.

Analysis of "Extreme Solar Events"

The paper "Extreme Solar Events" by Cliver et al. provides a comprehensive review of extreme solar activity phenomena, including both their historical origins and modern implications. The paper highlights distinct classes of solar outputs—sunspots, solar flares, coronal mass ejections (CMEs), geomagnetic storms, and solar energetic particle (SEP) events. The authors analyze both the observed instances and theoretical constructs to explore the limits of solar activity, exploring the resulting terrestrial impacts.

Historical and Theoretical Context

The research traces back to the 1859 Carrington Event, the most powerful geomagnetic storm on record. This seminal event provides a reference point for evaluating the magnitude of solar disturbances. The paper methodically develops a timeline of scientific understanding from the 19th century to contemporary analyses, highlighting the evolution of research interest in extreme solar phenomena, encouraged partly by technological vulnerabilities.

Key Findings and Observations

• Sunspot Groups: The paper addresses the probability distribution of large sunspot groups, with a specific focus on estimating 100- and 1000-year events. By analyzing sunspot areas from historical and ongoing observations, the research posits maximum sunspot group sizes on centennial and millennial scales, establishing key parameters within which these features can occur.
• Solar Flares and Superflares: A critical examination of solar flares reveals that the Sun can produce larger flares than those directly observed in modern times. By extending the probability distributions for X-ray fluxes, the paper estimates the plausible size of unprecedented flares. The authors also consider superflares from Sun-like stars, suggesting that understanding such stellar phenomena can inform limits on solar activity, though the current Sun may be less active than its peers.
• Coronal Mass Ejections: The paper highlights the energy and speed distributions of CMEs, employing a vast dataset from satellites to underpin theoretical projections for extraordinary events. It notes the implication of CMEs in both directly observed space weather and hypothetical extreme scenarios.
• Geomagnetic Storms: Using historical and modern geomagnetic indices, the research infers the extent of geomagnetic disturbances, with particular emphasis on historic events like the Carrington Storm. By correlating auroral latitudes with storm intensities, the authors provide a framework for estimating the power of geomagnetic storms over extended intervals.
• Solar Energetic Particles: The discussion on SEP events emphasizes the potential for rare, extraordinarily powerful occurrences like the proposed 774 AD event, inferred from cosmogenic isotopes. It mentions that while these are typically tied to CME-driven shock waves, certain historical spikes suggest enormity currently unseen in the directly measured solar record.

Implications and Future Perspectives

The paper underscores the significance of extreme solar events as not just subjects of academic inquiry but as phenomena with direct implications on space weather resilience for technology-reliant societies. By identifying and speculating on the existence of rare, high-magnitude phenomena—termed "dragon-kings"—the research expands the dialogue on the unpredictability and potential devastation of solar-induced effects.

Future developments should target refining predictive capabilities for space weather and advancing the scientific understanding of the underlying mechanisms of extreme solar activity. Enhancing our capacity to anticipate and mitigate the societal impacts of such events remains paramount, given the increasing dependence on technologies susceptible to solar disruptions.

Overall, the paper is a comprehensive synthesis of research on historical and modern records of extreme solar activity, applying statistical and theoretical modeling to address questions about the limits of solar phenomena and their implications on Earth.