SILSO Sunspot Number V1.0

The World Data Center SILSO (WDC SILSO) is the Center for the production, preservation and dissemination of the international sunspot number. The International Sunspot Number computed by the WDC SILSO measures the number of spots and groups of spots on the surface of the Sun every day through a worldwide network of observing stations according to a formula developped by R. Wolf in 1851 (Wolf, R.: 1851, Sonnenflecken-Beobachtungen in der zweiten Hälfte des Jahres 1850. Mitt. Nat.forsch. Ges.
Bern 207, 89.). This version is called the Zürich sunspot number series (or Sunspot Number version 1.0). In 2015, version 1.0 was discontinued and replaced by a new improved version (version 2.0) that includes several corrections of past inhomogeneities in the time series described in (Clette, F., Svalgaard, L., Vaquero, J.M., Cliver, E. W., 2014: Revisiting the Sunspot Number. A 400-Year Perspective on the Solar Cycle, Space Science Reviews, Volume 186, Issue 1-4, pp. 35-103. DOI: 10.1007/s11214-014-0074-2; Clette, F., Lefèvre, L., 2016, The New Sunspot Number: assembling all corrections, Solar Physics, 291, DOI: 10.1007/s11207-016-1014-y; Clette, F., Lefèvre, L., Cagnotti, M., Cortesi, S., Bulling, A., 2016: The Revised Brussels-Locarno Sunspot Number (1981 - 2015), Solar Physics, 291, DOI: 10.1007/s11207-016-0875-4 and Clette, F., Cliver, E.W., Lefèvre, L, Svalgaard, L., Vaquero, J.M., Leibacher, J.W., 2016: Preface to Topical Issue: Recalibration of the Sunspot Number, Solar Phys., 291, DOI: 10.1007/s11207-016-1017).