Relative sunspot number

From Glossary of Meteorology
(Redirected from Wolf-wolfer number)

relative sunspot number

A daily, calculated index of sunspot activity derived in part from the number of individual spots (umbrae), sunspot groups, and an applicable observatory factor. The standard international relative sunspot number (RI) is now derived at the World Data Center–Sunspot Index and Long-Term Solar Observations (SILSO) at the Royal Observatory of Belgium in Brussels.

Space Weather Prediction Center, 2018: Sunspots/solar cycke. Accessed 1 October 2018. Available at

Term edited 1 October 2018.