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arXiv · 2505.08832

A Possible Problem with the Sunspot Number

Leif Svalgaard
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Abstract

Sunspots are areas of strong magnetic fields driven by a convective dynamo. Rudolf Wolf devised his Sunspot Number (SN) series to describe its variation with time. Most other solar phenomena vary in concert with SN, in particular the microwave radiation. During the interval 2014-Jul to 2015-Dec, the variation of the SN with the microwave flux (e.g. F10.7) was anomalous, although microwave flux did not exhibit any anomaly with respect to the solar magnetic field measured by the HMI instrument on the SDO spacecraft. This points to a possible problem with the derivation of the SN using the 148,714 reports of sunspot observations received by the World Data Center Solar Influences (SIDC/SILSO at ROB) since 2011 (when the last public raw data was released). The unavailability of the raw data since then, contrary to avowed open data policy of ROB, prevents independent assessment and possible correction of the anomaly. We urge ROB to make the raw data available.

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Leif Svalgaard. 2025-05-13. A Possible Problem with the Sunspot Number. https://arxiv.org/abs/2505.08832

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