[Paper Review] Updating the Historical Sunspot Record

Leif Svalgaard|arXiv (Cornell University)|Mar 24, 2010

Solar and Space Plasma Dynamics7 citations

TL;DR

The paper argues that Rudolf Wolf's calibration of the Sunspot Number is accurate, while Max Waldmeier's 1945 adjustment introduced an artificial upward jump. Correcting for this jump reveals no long-term secular trend in sunspot numbers since the Maunder Minimum, implying solar activity has remained relatively stable over the past three centuries.

ABSTRACT

We review the evidence for the argument that Rudolf Wolf's calibration of the Sunspot Number is likely to be correct and that Max Waldmeier introduced an upwards jump in the sunspot number in 1945. The combined effect of these adjustments suggests that there has been no secular change in the sunspot number since coming out of the Maunder Minimum ~1700.

Motivation & Objective

• To evaluate the validity of Rudolf Wolf's calibration of the Sunspot Number.
• To investigate whether Max Waldmeier's 1945 adjustment introduced a spurious increase in sunspot numbers.
• To assess whether the historical sunspot record shows a secular trend since the Maunder Minimum.
• To reconcile discrepancies in historical sunspot data by correcting for methodological shifts.

Proposed method

• Reviewing historical observational records and calibration methods used by Wolf and Waldmeier.
• Comparing sunspot number series before and after Waldmeier's 1945 recalibration.
• Analyzing the consistency of Wolf's methodology with pre-19th century sunspot observations.
• Assessing the impact of the Waldmeier adjustment on long-term trends in solar activity.

Experimental results

Research questions

• RQ1 Is Rudolf Wolf's calibration of the Sunspot Number reliable and consistent with historical observations?
• RQ2 Did Max Waldmeier's 1945 adjustment introduce an artificial upward jump in the sunspot number series?
• RQ3 Is there evidence of a secular increase in sunspot numbers since the Maunder Minimum?
• RQ4 How does correcting for the Waldmeier adjustment affect the interpretation of long-term solar activity trends?

Key findings

• Rudolf Wolf's calibration of the Sunspot Number is supported as accurate by historical evidence.
• Max Waldmeier's 1945 adjustment introduced a significant upward jump in the sunspot number series.
• After correcting for the Waldmeier jump, no secular increase in sunspot numbers is observed since the Maunder Minimum.
• The corrected record indicates that solar activity has remained relatively stable over the past three centuries.