Smoothed Sunspot Number Calculation|
The daily sunspot number has little, if any, relationship to ionospheric variability.
However, the most widely used Ionospheric Index, R12, is derived from the daily sunspot
numbers. The R12 index is a twelve-month smoothed relative sunspot number.
To calculate the R12 index for July 2020, add half of the January 2020 value plus the
sum of the February through December 2020 values plus half of the January 2021 value and then by dividing that sum by twelve.
(where n1 = Jan 2020, n7 = July 2020 and n13 = Jan 2021)