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Current Sunspot Number: Insights from Recent Research
Understanding Sunspot Numbers: Historical Context and Modern Calibration
Sunspot numbers are a crucial index for understanding solar activity, particularly the 11-year solar cycle. Historically, two main forms of sunspot numbers have been used: the International Sunspot Number (ISN) initiated by R. Wolf in 1849, and the Group Sunspot Number (GSN) constructed by Hoyt and Schatten in the late 20th century1 2. These two series, however, have discrepancies that have led to confusion in solar studies, prompting recent efforts to recalibrate and correct these records1 2.
Recent Recalibration Efforts: Addressing Inhomogeneities
Recent workshops and studies have focused on diagnosing and correcting biases in both the ISN and GSN. Key periods of inhomogeneity identified include 1880-1915 for the GSN and 1947 and 1980-2014 for the ISN1 2. These corrections have led to a more accurate and consistent sunspot number series, eliminating significant rising trends in solar cycle amplitudes that were previously observed3. This recalibration is crucial for accurate long-term solar activity studies and has transformed the sunspot number archive into a dynamic, continuously improving dataset3.
Hemispheric Sunspot Numbers: North-South Asymmetries
A significant aspect of sunspot number studies is the hemispheric sunspot numbers (HSNs), which reveal north-south asymmetries in solar activity. Research has shown that the two hemispheres can exhibit decoupled behavior over the solar cycle, with phase shifts of up to 28 months between their peaks4. This decoupling aligns with dynamo theories and suggests that solar cycle predictions can be improved by considering the hemispheric dynamics separately4.
Conclusion
The recalibration of sunspot numbers and the study of hemispheric asymmetries provide a more accurate and nuanced understanding of solar activity. These advancements are essential for contemporary solar research and have significant implications for predicting solar cycles and understanding their impact on Earth's climate.
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Most relevant research papers on this topic
Revisiting the Sunspot Number
The newly revised Sunspot Number reveals a progressive decline in solar activity before the Maunder Minimum, suggesting that by mid-18th century, solar activity had already returned to levels equivalent to those observed in recent solar cycles in the 20th century.
Highly CitedRevisiting the Sunspot Number
The newly corrected sunspot number series improves our understanding of solar activity over the last 400 years, indicating a more stable 11-year cycle and a more consistent solar dynamo model.
Highly CitedThe New Sunspot Number: Assembling All Corrections
The new sunspot number, based on various diagnostics and corrections, eliminates the significant rising secular trend in solar-cycle amplitudes and transforms the data archive into a living observational series open to future improvements.
Highly CitedHemispheric sunspot numbers 1874–2020
The solar cycle evolves independently in the two hemispheres, with the northern hemisphere reaching its cycle maximum earlier, and empirical solar cycle prediction methods can be improved by investigating sunspot number evolution.
Millennium-scale sunspot number reconstruction: evidence for an unusually active sun since the 1940s.
The period of high solar activity during the last 60 years is unique in the past 1150 years, with a record of (10)Be concentration in polar ice providing evidence for this conclusion.
Highly CitedA Revised Collection of Sunspot Group Numbers
The revised collection of sunspot group numbers from 1610 to the present provides a greater estimate of solar activity than the original Hoyt and Schatten data, while maintaining a grand minimum of solar activity.
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