Monthly Ri Report

:Issued: 2026 May 01 08:35 UTC
:Product: documentation at http://www.sidc.be/products/ri 
#-------------------------------------------------------------#
# MONTHLY TABLE OF THE INTERNATIONAL TOTAL SUNSPOT NUMBER     #
# AND 12-MONTH PREDICTIONS from the World Data Center SILSO   #
#-------------------------------------------------------------#

Provisional International monthly mean Sunspot Number for
April 2026 : 79.3 (seventy-nine point three)

Maximum : 135 on 30 // Minimum : 28 on 10

Provisional daily International Sunspot Numbers for April 2026 : 

      1..129    6.. 97   11.. 39   16.. 50   21.. 50   26..115
      2..133    7.. 89   12.. 38   17.. 48   22.. 71   27..117
      3..120    8.. 70   13.. 53   18.. 41   23.. 68   28..128
      4..106    9.. 59   14.. 53   19.. 36   24.. 94   29..123
      5.. 89   10.. 28   15.. 49   20.. 37   25..114   30..135

68 cooperating stations on May 1, 09 UT

Predictions of the monthly smoothed Sunspot Number using the last
provisional value, calculated for October 2025 : 108.3 (+-5%)

            SM    CM                 SM    CM                 SM    CM     

2025 Nov   109   108     2026 May    91   107     2026 Nov    77    99
     Dec   105   109          Jun    89   106          Dec    75    95
2026 Jan    98   110          Jul    87   103     2027 Jan    72    92
     Feb    97   110          Aug    85   102          Feb    69    88
     Mar    95   110          Sep    83   101          Mar    66    85
     Apr    93   109          Oct    80   100          Apr    64    82

SM : SIDC classical method : based on an interpolation of Waldmeier's
standard curves; the estimated error ranges from 7% (first month) to
35% (last month)
CM : Combined method : the combined method is a regression technique
coupling a dynamo-based estimator with Waldmeier's idea of standard
curves, due to K. Denkmayr.
ref. : K. Denkmayr, P. Cugnon, 1997 : "About Sunspot Number Medium-Term
Predictions", in "Solar-Terrestrial Prediction Workshop V", eds.
G. Heckman et al., Hiraiso Solar Terrestrial Research Center, Japan, 103



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