Kalugodu, Chandrashekhar ; Lefèvre, Laure ; Mampaey, Benjamin ; Valliappan, Senthamizh Pavai ; Hayakawa, Hisashi ; Ritter, Christian

Poster presented at European Space Weather Week 2025, Umea (Sweden) on 2025-10-31

Abstract: The International Sunspot Number (SN) remains affected by historical scale jumps such as the Waldmeier break, even after two major recalibrations. FARSuN (Findability and Accessibility of historical Raw Sunspot Numbers) tackles this by rebuilding the record from the ground up: collecting handwritten logs and tables from 1607–1980, digitizing them, and applying consistent metadata and validation. The reconstructed SN V3 will deliver traceable uncertainties, hemispheric indices, and open FAIR-compliant access, strengthening space climate studies, solar cycle prediction, and coupled Sun–Earth research.

Keyword(s): International Sunspot Number ; SN V3 ; FARSuN ; Solar activity reconstruction ; Waldmeier break ; Historical sunspot observations ; Space climate ; Solar cycle calibration ; Data digitization ; FAIR data principles