A Possible Problem with the Sunspot Number

TL;DR

The paper identifies an anomaly in the Sunspot Number series during 2014-2015, suggesting a potential issue in its derivation process, which hampers independent verification and correction.

Contribution

It highlights a possible flaw in the Sunspot Number data collection process and calls for transparency by making raw data publicly available.

Findings

Anomalous correlation between Sunspot Number and microwave flux in 2014-2015

No anomaly observed in microwave flux relative to solar magnetic field

Lack of raw data prevents independent verification of Sunspot Number anomalies

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.